Some may disagree, but I think the Breath of the Wild / Tears of the Kingdom continuity demands an epic conclusion. Tears ended on a great note, but Zelda and the Sages' job was clearly unfinished. The castle is still in shambles. Master Kohga is still out there. The Kingdom of Hyrule still needs restoration - and it needs a Queen.
With all that unfinished business (and the two games' unparalleled success), Nintendo would be insane not to complete this trilogy. What might that look like?
Title
Properly completing the trilogy starts with a title that parallels the others. "Breath of the Wild" and "Tears of the Kingdom" - breath and tears are both things that naturally come out of a body. The only other thing I can think of that fits this category (that would be appropriate for a game title at least...) is blood. So, blood of the what?
Many have probably already reached the same conclusion as me by this point -
Blood of the Goddess
This title would refer to none other than Zelda herself (who has never been directly referenced in a game subtitle before), and specifically her relation to Hylia. The term was spoken explicitly by Demise at the end of SS, and a similar term was spoken by Impa in BOTW when explaining the history of Calamity Ganon. Therefore it would be widely recognized and fit in the context of the franchise.
Themes
If Breath depicted the fall of the kingdom, and Tears the founding, then Blood surely should depict the restoration and the full and final awakening of Zelda's power, i.e., the Triforce that lives within her that she until now has only been able to channel in subtle ways. Yes, the Triforce – conspicuously absent from the last two games – should make a grand reappearance.
The kingdom's restoration and the awakening of the Triforce would be linked to one another metaphorically and literally. Major campaigns ("dungeons") in Lanayru, Eldin, and Faron would result in rediscovery/reawakening of the Triforce of Wisdom, Power, and Courage, respectively. An unprecedented - but IMO long overdue - move would be to allow the player to actually use each Triforce piece, once awakened, as an in-game ability. Much like ultrahand, cryonis, etc., unlocking each Triforce could give the player abilities thematically related to power, wisdom, and courage, that would facilitate the restoration of different aspects of the kingdom:
Power - building structures, reshaping land
Wisdom - order, society, government
Courage - life, spirit, kindness
The "shrines" in this game would be, say, 156 tests of power, wisdom, or courage (52 each), that would bit by bit restore power to the Triforce and, in turn, allow it to be used to help restore different aspects of the kingdom from buildings to social structure to injured or sick individuals (along with every 4 shrine rewards opening up an obligatory heart container or stamina vessel).
The Triforce, however, would not be capable of full physical restoration at any point in the game (possessing an omnipotent artifact doesn't make for a very interesting plot), but it will be revealed that something is blocking its full potential.
Zelda must be an integral character in this process. While it is unlikely Aonuma & Co. will ever relent and make her playable, she should exist as an interactive character in the present for the entire game, not as a trapped damsel nor in the past nor through mere memories.
Also associated with blood is sacrifice - thus a beloved character should die at the conclusion of this game as a sacrifice to destroy the ultimate evil (see below).
Villain and Plot
First off, the villain must not be Ganon(dorf). A third appearance of this, frankly, one-dimensional character in a row would add little by way of drama at this point and cheapen the apparent triumph in Tears.
At first, the villain should not be obvious. As you begin the quest to restore the Kingdom, you will gradually learn that a force is at work trying to stop you and is keeping the Kingdom corrupted. Buildings, even after being rebuilt, continue to crumble (anti-power), towns and governments cannot seem to stay stable (anti-wisdom), and the people suffer from despair and illness (anti-courage).
At some point in the first half of the game, you learn that Kohga and the Yiga clan appear to be responsible for the continued blight. Kohga is no longer a joke. He is doing serious damage and responsible for many deaths and much despair, and rumor is he is trying to unlock an ancient power to corrupt or even destroy the Triforce. Eventually the quest becomes one to find him and bring him to justice.
Once the Triforce has been reassembled and Hyrule put right on the path toward restoration (about 2/3 through the game), Kohga is confronted and, in a rage, despite knowing he should take him back alive to face justice, Link slits his throat with the Master Sword, killing him, as though a dark power momentarily possessed him to do so.
At this point the twist is revealed. In a quest to avenge his master, Kohga had learned of the true nature of Ganondorf's power - the demigod Demise - along with that of Zelda's (literally the blood of the goddess) and Link's (the spirit of the hero). He also knew that Demise's remnant lived on within the Master Sword. Through black magic he devised a way to restore Demise and thus end the world - when the Master Sword spills human blood in anger, the evil trapped within will be reempowered and resurrected.
Thus the Hero's commission of the ultimate anti-courageous act using the Sword of the Goddess - murder - has the effect of restoring Devise, who reveals that from within the Master Sword he has watched for eons, in disgust, as those with the Blood of the Goddess and the Spirit of the Hero squander their gifts to empower the weak and make impotent the strong. His sole desire is to end the bloodline of Hylia permanently, to destroy the Triforce (which he of course cannot use), and to send the world into eternal night.
However, Demise is not the only being in the Master Sword who is revived through this event. Fi awakens from her eternal sleep to whisk Link and the sword away before Demise can destroy them. They return to Zelda, where they determine the steps for the endgame and final confrontation.
The final “real” battle is of course a rematch between the Hero and Demise. For the "cinematic" battle, Zelda uses the Triforce to reawaken her inner power and reemerge as Hylia – in her “glorious” (Demise’s words) divine form, battling Demise in the sky, with Link paragliding alongside providing support (a twist on the prior two cinematic battles in which Zelda supports Link), essentially a rematch of the ancient battle referenced in Skyward Sword between Hylia and Demise with the Hero at her side.
As before, of course, Demise is only defeated but cannot be destroyed through force alone and is once again absorbed into the Master Sword. However, the group realize that mere imprisonment is not an option, as Demise will always just return in some form and/or in the future, manipulating countless "Gannondorf's" along the way to do his bidding. Fi therefore explains that this time, the Master Sword itself must be destroyed - which can only be done – how else? – by casting it back into the fire from which it was forged - Eldin volcano. In a heartbreaking scene, Fi says farewell to the present Link, with the ghosts of all the prior Heroes and wielders of the sword looking on, as he tearfully tosses the sword into the lava.
As Demise's shadow rises from the melting sword and dissipates into the ether, the final curse blocking the Triforce’s efficacy and preventing Hyrule's restoration is lifted. The physical Triforce fully rematerializes high above the caldera, and light spreads over the entire kingdom, restoring the Castle, Castle Town, and the rest of the Kingdom, with the Triforce itself seemingly dissipating throughout the world.
In the final "true" ending (after-credits scene), Zelda is crowned Queen, with Link by her side, both with visible glowing Triforce symbols on their hands, to suggest that the Blood of the Goddess (Triforce of Wisdom) and Spirit of the Hero (Triforce of Courage) live on in them. After a fade, a dimly lit nondescript place is seen, occupied by an equally dimly lit person, whose only visible feature is a hand depicting the Triforce of Power. To whom has Din now chosen to gift her power, and for good or ill?
Why this probably won't happen (even if it should)
Unfortunately, an epic story with this level of drama probably won't happen. While Skyward Sword had arguably the most intricate and dramatic story of any Zelda game, many consider its gameplay to have suffered as a result. Aonuma has since taken an unapologetically opposite "gameplay first, story last" approach with Breath and Tears. Moreover, an explicit acknowledgement of the canon of any game prior to Breath - even Skyward Sword - would be inconsistent with Aounuma's apparent intent to use Tears of the Kingdom to retcon the entire franchise.
For these reasons, I would predict any third installment: 1) would have to be just as open-ended in terms of the quest as Breath and Tears, with only minimal major inflection points that must proceed in a specific order; and 2) would not rely too heavily on canon from games prior to Breath of the Wild.
On the other hand, Tears did demonstrate a willingness to bring in some drama and mandatory-quest-order items (e.g. you cannot unlock the castle “dungeon” and dehydrated Ganondorf’s dramatic reveal before finishing the four regional quests). Skyward Sword also seems like the game that Aonuma is most willing to maintain as canon, with both Breath and Tears clearly referencing an entity living in the Master Sword, and a reference in Breath (by Impa) to an “ancient evil that is reborn time and time again.” Still, acknowleding that any events in SS actually happened literally as depicted in the prior game would be a first for this sub-franchise.
Regardless, I hope reading this sparks some imagination, excitement, and support for a third installment.
With all that unfinished business (and the two games' unparalleled success), Nintendo would be insane not to complete this trilogy. What might that look like?
Title
Properly completing the trilogy starts with a title that parallels the others. "Breath of the Wild" and "Tears of the Kingdom" - breath and tears are both things that naturally come out of a body. The only other thing I can think of that fits this category (that would be appropriate for a game title at least...) is blood. So, blood of the what?
Many have probably already reached the same conclusion as me by this point -
Blood of the Goddess
This title would refer to none other than Zelda herself (who has never been directly referenced in a game subtitle before), and specifically her relation to Hylia. The term was spoken explicitly by Demise at the end of SS, and a similar term was spoken by Impa in BOTW when explaining the history of Calamity Ganon. Therefore it would be widely recognized and fit in the context of the franchise.
Themes
If Breath depicted the fall of the kingdom, and Tears the founding, then Blood surely should depict the restoration and the full and final awakening of Zelda's power, i.e., the Triforce that lives within her that she until now has only been able to channel in subtle ways. Yes, the Triforce – conspicuously absent from the last two games – should make a grand reappearance.
The kingdom's restoration and the awakening of the Triforce would be linked to one another metaphorically and literally. Major campaigns ("dungeons") in Lanayru, Eldin, and Faron would result in rediscovery/reawakening of the Triforce of Wisdom, Power, and Courage, respectively. An unprecedented - but IMO long overdue - move would be to allow the player to actually use each Triforce piece, once awakened, as an in-game ability. Much like ultrahand, cryonis, etc., unlocking each Triforce could give the player abilities thematically related to power, wisdom, and courage, that would facilitate the restoration of different aspects of the kingdom:
Power - building structures, reshaping land
Wisdom - order, society, government
Courage - life, spirit, kindness
The "shrines" in this game would be, say, 156 tests of power, wisdom, or courage (52 each), that would bit by bit restore power to the Triforce and, in turn, allow it to be used to help restore different aspects of the kingdom from buildings to social structure to injured or sick individuals (along with every 4 shrine rewards opening up an obligatory heart container or stamina vessel).
The Triforce, however, would not be capable of full physical restoration at any point in the game (possessing an omnipotent artifact doesn't make for a very interesting plot), but it will be revealed that something is blocking its full potential.
Zelda must be an integral character in this process. While it is unlikely Aonuma & Co. will ever relent and make her playable, she should exist as an interactive character in the present for the entire game, not as a trapped damsel nor in the past nor through mere memories.
Also associated with blood is sacrifice - thus a beloved character should die at the conclusion of this game as a sacrifice to destroy the ultimate evil (see below).
Villain and Plot
First off, the villain must not be Ganon(dorf). A third appearance of this, frankly, one-dimensional character in a row would add little by way of drama at this point and cheapen the apparent triumph in Tears.
At first, the villain should not be obvious. As you begin the quest to restore the Kingdom, you will gradually learn that a force is at work trying to stop you and is keeping the Kingdom corrupted. Buildings, even after being rebuilt, continue to crumble (anti-power), towns and governments cannot seem to stay stable (anti-wisdom), and the people suffer from despair and illness (anti-courage).
At some point in the first half of the game, you learn that Kohga and the Yiga clan appear to be responsible for the continued blight. Kohga is no longer a joke. He is doing serious damage and responsible for many deaths and much despair, and rumor is he is trying to unlock an ancient power to corrupt or even destroy the Triforce. Eventually the quest becomes one to find him and bring him to justice.
Once the Triforce has been reassembled and Hyrule put right on the path toward restoration (about 2/3 through the game), Kohga is confronted and, in a rage, despite knowing he should take him back alive to face justice, Link slits his throat with the Master Sword, killing him, as though a dark power momentarily possessed him to do so.
At this point the twist is revealed. In a quest to avenge his master, Kohga had learned of the true nature of Ganondorf's power - the demigod Demise - along with that of Zelda's (literally the blood of the goddess) and Link's (the spirit of the hero). He also knew that Demise's remnant lived on within the Master Sword. Through black magic he devised a way to restore Demise and thus end the world - when the Master Sword spills human blood in anger, the evil trapped within will be reempowered and resurrected.
Thus the Hero's commission of the ultimate anti-courageous act using the Sword of the Goddess - murder - has the effect of restoring Devise, who reveals that from within the Master Sword he has watched for eons, in disgust, as those with the Blood of the Goddess and the Spirit of the Hero squander their gifts to empower the weak and make impotent the strong. His sole desire is to end the bloodline of Hylia permanently, to destroy the Triforce (which he of course cannot use), and to send the world into eternal night.
However, Demise is not the only being in the Master Sword who is revived through this event. Fi awakens from her eternal sleep to whisk Link and the sword away before Demise can destroy them. They return to Zelda, where they determine the steps for the endgame and final confrontation.
The final “real” battle is of course a rematch between the Hero and Demise. For the "cinematic" battle, Zelda uses the Triforce to reawaken her inner power and reemerge as Hylia – in her “glorious” (Demise’s words) divine form, battling Demise in the sky, with Link paragliding alongside providing support (a twist on the prior two cinematic battles in which Zelda supports Link), essentially a rematch of the ancient battle referenced in Skyward Sword between Hylia and Demise with the Hero at her side.
As before, of course, Demise is only defeated but cannot be destroyed through force alone and is once again absorbed into the Master Sword. However, the group realize that mere imprisonment is not an option, as Demise will always just return in some form and/or in the future, manipulating countless "Gannondorf's" along the way to do his bidding. Fi therefore explains that this time, the Master Sword itself must be destroyed - which can only be done – how else? – by casting it back into the fire from which it was forged - Eldin volcano. In a heartbreaking scene, Fi says farewell to the present Link, with the ghosts of all the prior Heroes and wielders of the sword looking on, as he tearfully tosses the sword into the lava.
As Demise's shadow rises from the melting sword and dissipates into the ether, the final curse blocking the Triforce’s efficacy and preventing Hyrule's restoration is lifted. The physical Triforce fully rematerializes high above the caldera, and light spreads over the entire kingdom, restoring the Castle, Castle Town, and the rest of the Kingdom, with the Triforce itself seemingly dissipating throughout the world.
In the final "true" ending (after-credits scene), Zelda is crowned Queen, with Link by her side, both with visible glowing Triforce symbols on their hands, to suggest that the Blood of the Goddess (Triforce of Wisdom) and Spirit of the Hero (Triforce of Courage) live on in them. After a fade, a dimly lit nondescript place is seen, occupied by an equally dimly lit person, whose only visible feature is a hand depicting the Triforce of Power. To whom has Din now chosen to gift her power, and for good or ill?
Why this probably won't happen (even if it should)
Unfortunately, an epic story with this level of drama probably won't happen. While Skyward Sword had arguably the most intricate and dramatic story of any Zelda game, many consider its gameplay to have suffered as a result. Aonuma has since taken an unapologetically opposite "gameplay first, story last" approach with Breath and Tears. Moreover, an explicit acknowledgement of the canon of any game prior to Breath - even Skyward Sword - would be inconsistent with Aounuma's apparent intent to use Tears of the Kingdom to retcon the entire franchise.
For these reasons, I would predict any third installment: 1) would have to be just as open-ended in terms of the quest as Breath and Tears, with only minimal major inflection points that must proceed in a specific order; and 2) would not rely too heavily on canon from games prior to Breath of the Wild.
On the other hand, Tears did demonstrate a willingness to bring in some drama and mandatory-quest-order items (e.g. you cannot unlock the castle “dungeon” and dehydrated Ganondorf’s dramatic reveal before finishing the four regional quests). Skyward Sword also seems like the game that Aonuma is most willing to maintain as canon, with both Breath and Tears clearly referencing an entity living in the Master Sword, and a reference in Breath (by Impa) to an “ancient evil that is reborn time and time again.” Still, acknowleding that any events in SS actually happened literally as depicted in the prior game would be a first for this sub-franchise.
Regardless, I hope reading this sparks some imagination, excitement, and support for a third installment.