I wonder if Pokémon Z/X2/Y2 will be the first "third version" to include substantial changes to the roster of Pokémon with new Mega Evolutions? Or, I wonder if they might be so bold as to include actual new Pokémon or evolutions?
Unlike previous gens, this is the first gen that could be updated via SpotPass. I don't expect GF to sell new Pokémon via DLC, but I would be excited to see Pokémon Z/X2/Y2 with full evolutions to Pokémon like Carbink, evolutions to older Pokémon like Dunsparce, and Mega Evolutions for all sorts of Pokémon (probably including the Gen VI starters, which would make for a nice marketing gimmick) with updates to X/Y to maintain compatibility.
Basically, I'm just hoping the new third version can be more substantial since there are no longer technical boundaries to maintaining compatibility.