Serebii has just confirmed that this months issue of CoroCoro has some more info on Pokemon Omega Ruby and Alpha Sapphire. I'll update this as more is revealed.
Steven Stone has the Mega Metagross which he evolves using his Mega Brooch. The scan also references that there are different Pokemon in Hoenn now. Presumably Kalos Pokemon and a few others from gens after 3.
Seems as though Steven is the Champion again, because screw Wallace.
Mega Metagross gains Tough Claws. Mother of pearl...