The Pokemon in the box screenshots revealed today I believe are getting Megas (if not evos). Most have already appeared in battle scenes. Tauros, Hariyama, Zoroark, Golurk, Snorlax, Gardevoir were all in the box with the new 6th Gen Pokes and of course Mawile, which we already know has a Mega.
Now, the other Pokes were Weavile, Gliscor, Dragonite, Gyarados, Machamp, Krookodile, Hydreigon, Miltank, Haxorus, Staraptor, Flygon, Druddigon, Scizor, Salamence, Haunter(Gengar), Lapras, Houndoor(Houdoom) which appeared alongside Ampharos and Absol who also have Megas. The third box showed Kingdra, Typhlosion, Metagross, Chandelure, Volcarona, Infernape, Pachirisu, Altaria, Swampert, Milotic, Ditto and a couple Legendaries.
I strongly believe most if not all of these Pokemon will receive Mega evolutions. They are very believable and GF is giving us a BIG hint!