UPDATE Since my last post here:
N-You'd have to be stupid to be asking that question now, especially after all the news that's been released.
Belle-Maybe, she is champion, but only for some time. I don't think they'll leave her out though.
Cheren-I don't think they will leave him out though, like what I said with Belle.
Both seem to play a main part in the story, so I don't see why not. Maybe they'll be reduced to being in the openings of movies where they show a Pokemon battle, like how Diamond was, and how Black and White will be.