Mega Beedrill (Bug/Poison; Adaptability) and Mega Pidgeot (Normal/Flying; No Guard) leaked by Corocoro!
Mega Latios/Latias as well!
http://www.serebii.net/index2.shtml
BEES. MY GOD.
Update! From Serebii: You can fly on Mega Latios & Latias in the overworld (!) and find Pokémon such as Reshiram, Zekrom, Dialga & Palkia in the sky (!!). Latios is exclusive to Omega Ruby and Latias is exclusive to Alpha Sapphire.
Update (2)! From Serebii: The Legendary Pokémon are found on islands that can only be found through areas on the sky. You access the sky through the Eon Flute item.