Whatever this "shocking twist" is, it probably won't be one of two things:
#1: Anything extravagant that references other games and whatnot.
#2: Most of what fans will bring up pre-release.
For instance, I doubt we'll be seeing a cutscene showing the Hero of Time's defeat which leads to the Downfall Timeline. Awesome though that would be, Zelda rarely references other games not directly related to it. Even games like Majora's Mask and Link's Awakening barely referenced Ocarina of Time and A Link to the Past respectively. An example of number two would be "Link returns to Hyrule, and it's the freaking Dark World, everybody!" Something like that is kind of expected.
Then again, Nintendo is looking to "rethink the conventions of Zelda," so for all we know, Barnes from Twilight Princess will burst in wielding a chaingun and tell Link he's his future son. I'd expect something a bit more conventional, yet still shocking. Perhaps it will suddenly be announced that Zelda is getting married, for instance, or that Sahasrahla passed away while Link was gone. Something genuinely shocking, but still within Zelda's fiber as it stands today. However it turns out, I'm looking forward to the big reveal.