At this point, I'm convinced that it's Gamefreak's way of eventually releasing an entire generation with no actual new Pokemon. They seem to be afraid of inflating the dex count too high already. Picture it now: a two region game, with 25-30 variant Pokemon per region and 25-30 new Megas.
"What? We thought you wanted regional variants, Megas, and a game with more than one region?" They're like genies, be careful what you ask for.