That would bring up the question why didn't Eevee evolve on burial grounds in previous games. You just HAVE to inroduce a new item, new mechanic, or just a new condition for evolution.
I think Black 2 and White 2 were announced during Pokémon Smash or whatever it was called back then
You know, I'm inclined to believe this new rumor from Vegetable Perap. It just brings so little actual new/massive info, that you can't help but believe it, unlike all those fakes who "leak" whole regions, new Pokémon, plot bits etc.