Well not really. Case in point, Mewtwo in Smash 4.
If they just show a model like they did in the 50 Fact-Extravaganza, it would work.
The difference between Mewtwo and whatever they may show at the TGA is monumental, though.
Mewtwo is an old character everyone is familiar with. He was in Melee, and he was only announced as such because he was heavily requested after it was said he wouldn't be in Smash 4, so his announcement at the 50 Fact-Extravaganza was simply to say "Hey, we're gonna work on him, you can stop asking." He didn't need to be a surprise or have a grand reveal because, well, we've seen him before.
Now imagine if they announced Cloud with just a character model. How lame and disrespectful would that be? Of course it'd still be exciting, because it's a big new character, but what a waste of a historic reveal. Same with Ridley--his reveal was so much better because of how amazing the trailer was, building up to him when all hope had been lost. Even Piranha Plant got his own trailer, even though his Final Smash clearly isn't finished yet, because just showing a model is a terrible way to reveal new fighters.
So it's confusing to me that people think that Nintendo is going to reveal Sora (or anyone else)
on-stage with nothing more than a model.