Take a look at this picture.
http://i.imgur.com/ouZ5wMl.jpg
The ages old theory that the evil team names spell out Gramps has finally come to fruition. However, there is one team that's excluded from this picture: Team Flare.
Why is Team Flare singled out? Well, it's simple. Remember how in ORAS Zinnia implied that gen 6 took place in a universe separated from the first 5 generations? The old universe doesn't have the "infinite energy" necessary to do things like warp a meteor, power the Ultimate Weapon, or trigger Mega Evolution.
If there is no infinite energy, then the war in Kalos never happened and Team Flare has no reason to exist. Since Team Flare is the only team that is excluded from this picture, it's safe to assume that Team Skull is in the original universe like the rest of the teams.
Which means Mega Evolution doesn't exist in Pokemon Sun and Pokemon Moon.
