This is a great topic. I've always liked the other races in Zelda games, and especially when they are a huge part of the story line such as OoT with the Kokiris and MM with the Dekus, Zoras, and Gorons. But Nintendo can't just be careless and throw a bunch of creatures in there for no apparent reason. They need to fit, and they fit perfectly in those two games in my opinion. I haven't really been paying much attention to recent Zelda news, so I don't really know much about the SS plot/storyline, but this is what Wikipedia says...
"
Skyward Sword is a prequel to
Ocarina of Time.
[9] The
Link appearing in the game was born and raised in Skyloft, a group of islands floating above the clouds.
[10][8][9] Leading an ordinary life there, he one day discovers the Skyward Sword, which leads him to another, previously unknown land beneath, ruled by evil forces.
[10] Using the sword to travel back and forth between the two worlds, the mystery of why they became separated is gradually revealed to Link.
[10] The Skyward Sword will turn into the Master Sword at some point in the game and, while giving Link advice, it will assume the form of the female figure in the concept art shown at E3 2009"
I think that judging by this, the Oocas could fit well. In TP, they were primarily located in the City in the Sky, and when I first heard of Skyloft that's immediately thought of. We have no way to know fully whether or not the Oocas will be there, and it's certainly up to debate. But if there is going to be a primary "other race", such as the Kokiri's were in OoT, that the best chance is that it will be the Oocas because of their connection to the sky.
As for the Deku's that we have briefly seen, it looks to be as they are just simple enemies, and that should mean that they will not have a gigantic role like they did in MM, but more like an OoT role. In OoT, they were simple enemies scattered across Hyrule, but there were also some that when you stunned, sold you items such as beans. I guess I'm happy to see that they will probably make some kind of resurgence, but for opinion, unlike some, they aren't that important. They're just another enemy, like an octorok, moblin, stalfos, whatever. They just may have a small variation, but it seems unlikely that they will have a major role in the storyline.
As for the Gorons and Zoras, and other tribes, I'd be quite surprised if the came up as enemies, but it would be a pleasant surprise. I don't remember the Gorons ever being enemies outside of what they were in TP, but if they were, someone could point that out to me. But if they did come up as enemies, I think that would be a pleasant surprise rather than an unpleasant surprise. With their abilities to roll up, eat rocks, or whatever else they might do, it would add a cool aspect, and a nice new enemy. However, that probably won't happen. It's more likely that they will be civil people that have some kind of village, such as they did in OoT and TP. If this is a prequel to OoT and probably TP (depending on your view of the timeline), then we might see some kind of village. There was a lava/fire oriented dungeon in the trailer, and it could have some association with the Gorons, which would suggest that there would be this village I'm talking about, but it could just be something like TWW, whose fire dungeon had no association with the Gorons, instead it was associated with the Rito tribe, who could possibly be some kind of evolution of the Zoras. As for other miscellaneous tribes such as the Shiekah, I could honestly care less about what they do. Maybe an appearance with a village would be nice, but most races seem like a small aspect of the games.
As for new races, my advice to Nintendo is to knock yourselves out, but don't go overboard. I don't need 20 new races hiding behind every tree. Most races, however, have been introduced as enemies, for example, the Zoras. They started out as an enemy in LoZ, but never really evolved into a civil people until OoT. SS may introduce enemies that become a civil race, or they may just make a new race that starts out civil. I could really care less. But if they introduce races and integrate them well, that is a huge thumbs up.
So, overall, races = good, but not great unless Nintendo does a good job of integrating them into the game/storyline in a fresh, interesting way.