I am glad everyone is finally getting on board with the Mega Evolutions, I think it is cool that GF is willing to go all out on this game. Also, with 3rd Gen remakes being the next games (hopefully ) I would think at least all the 3rd Gen starters would get one, but I honestly think that every starter will get a Mega Evolution.
Also, for competitive players, how long is it going to take to reconfigure all the tiers and stuff? Not only a new type is introduced, but now Mega Evolutions? This is the most hyped I have been for a Pokemon game since Emerald and my hype train left the station long ago, October really does need to hurry!
It took about a year and a half for BW to solidify and 6 months or so after B2W2. It's probably going to be even longer this time considering how radically things are going to be altered, with this and a new type as well as the new generation's worth of pokemon to sort out.