>>21676124One of Pokemon's scenario writers already posted a timeline on twitter.
RBY = RSE -> GSC = DPP -> BW -> B2W2 = XY
Presumably all remakes are still the same time as the original.
IIRC, Mega Evolution can only happen in Kalos because reasons, so let's just assume it's been retconned to happen in Hoenn too, but not Kanto, Johto, Sinnoh, or Unova.