CoroCoro magazine just revealed 3 new Mega Pokemon and they will be in the upcoming new games Pokémon Omega Ruby & Alpha Sapphire which will be released worldwide in November 2014. The 3 new Mega Pkmn are:
Mega Sceptile, Mega Swampert and Mega Diancie.
this means all HOENN starters will have a Mega Evo!
"Mega Sceptile is Grass/Dragon-type while the others maintain their type. Mega Diancie's ability is currently listed as ??? while Mega Sceptile has Lightning Rod and Mega Swampert has the ability Swift Swim. "