Plus, there is the reference to White Forest in Black, and to Black City in White, as well as the aesthetic and cultural differences between the two versions of Unova (one values technology, while the other values nature).I think the first in-game reference to that was in BW. There's a guy in Opelucid City who makes mention of the opposite version of the city, and wants you to find him Pokemon with Charge from the "other world" (the opposite game).
About the same, but with Megas.The big question is, how do the events of other generations play out in the Mega Evolution universe?
Kanto, Johto, Sinnoh, and Unova Confirmed!!
For instance, FRLG in this universe probably looks a lot like Pokémon Origins. And we know that Team Plasma was active in the Unova region some time before XY.