Playable Pokémon selection is gonna be interesting.
We've got Pikachu, Charizard, Lucario and Greninja confirmed so far (nice variety of types there!) Four of them. Now, Jiggly, I'd like to think Jiggly's a shoe-in because of seniority. All speculation here, but let's count Jiggs in, which takes up to five spots.
Then it gets complicated. While I find it very odd that Squirtle and Ivysaur (both of which brought unique movesets and mechanics to the table) would be cut just like that, if Sakurai really only could bring one of the PT's Pokemon back, of course he'd go with Charizard due to the dragon's popularity.
I think it's natural to think then, that either both Squirtle and Ivysaur are gone, or both are back, because I can't see them bringing back 2 of PT's Pokémon and just forgetting about the other.
Then again, Mewtwo's had a resurgence as of late. Had a role in Pokémon Origins, had new movie appearances, the only Pokémon sans Charizard to get 2 Mega Evolutions in X/Y...Hell, Sakurai has even nodded in Mewtwo's direction already:
Pikachu, Charizard, Lucario, Greninja, Jigglypuff and Mewtwo would make 6 spots. Six individual spots may be about the limit for a single franchise, and if Sakurai brought Ivysaur and Squirtle back on top of this, that'd be eight spots for Pokémon alone, and I have my doubts about Sakurai allowing Pokémon to take over that large a percentage of the final roster. Hmmm....