Before I start rambling on, I'd like to clear a few things up:
I LOVE the Pokemon Anime--especially the older episodes! I'm kind of iffy on the most recent season, but I still enjoy it enough to watch it. Ash is a great character!
I, also, love the Pokemon games! I think I enjoy the games even more than the show, and that's saying something.
Anyways... Time to get started!
I liked it when the game inspired the show. I've played through all the games, and seeing it come to life in a cartoon was brilliant! I don't know why, but the anime influencing the game kind of bugs me... Unless GameFreak gave that idea to the makers of the anime, then I'm not happy.
Greninja is one of the few XY Pokemon that I like... However, I don't think it deserves all the attention its getting. Sure, it has a neat design; sure, its in-game moveset is incredible, but it seems like people have forgotten about all of the older and (this is arguable) better Pokemon.
Speaking of Greninja's incredible moveset, why is it getting an upgraded form? It's already very, very strong... Does it really need to get stronger?
The last thing I'd like to say is I'm kind of hoping it's considered a mega evolution (and I strongly dislike mega evolutions as they are), rather than an 'Ash' or 'bond' evolution. That doesn't make too much sense to me - especially 'Ash' evolution.
It felt good to get that out of my system. {XD}
TL/DR: I disagree with GameFreak's choice of adding Ash-Greninja to Pokemon Sun and Moon.