Well, almost everything I wanted to say about this has already been said.
While I like mega evolutions, I'm hoping for an actual evolution this time. Whether it's an evolution based off a Kalos Pokemon or an older Pokemon is fine by me. I'm leaning towards an evolution for an older Pokemon (*coughdunsparceorqwilfishoreeveecough*). If it is based off a Kalos Pokemon, I'm hoping it's Helioptile, as I plan on using it for my team. I won't care if it's a brand new Pokemon that will have pre-evolutions, like Noivern, but I doubt it will happen.
If this is a new Pokemon, and not a mega evolution, that will make it new Pokemon #40. :] I hope they leave it at that and have the rest be discovered upon release.