I hope that this movie is solely about Xerneus while the next is about Yveltal with the 3rd being about both and maybe the 3rd member if there is one. It's unlikely but that's how I would want it to be.
Wonder if the pokemons on that picture will be on the main cast in the movie?
It seems likely as Inkay, Fletchling, Froakie, Dedenne and Bunnelby is confirmed for main cast already and we got hints about that Pancham may be there too.
The main legendaries are probably Xerneas and/ or Yveltal and the cutesy event legend. Watch the random Pokemon in the ads just make cameos.
Remember, although, that the first Zoroark movie teaser had the Gold and Silver mascots battling when they were nowhere to be found in the body of the film. Ho-Oh still hasn't shown up in a movie outside of intros and a transformed Mew. (and then Celebi and Suicune showed up again in that movie)
Likely not. They usually keep third version/sequel/whatever mascots (which Zygarde almost certainly is) for the second movie of a generation. Now they might shake that up this gen, but at the moment we have no reason to believe they will.
This seems to confirm that the water starter curse is not going to be broken for the forseeable future. Does this mean that the writers are planning to lock Froakie into his first stage form for the entire series?