Have a not so great scan
Pokemon Omega Ruby and Alpha Sapphire can add another Mega Evolution to their stable, courtesy of this scan from CoroCoro and Serebii explanation.
"It revealed Mega Metagross, which will be used by Steven. Steven Mega Evolves Metagross using the Mega Brooch, and the scan references the fact that there are different Pokémon in Hoenn than before."
Not sure how correct that is as I have never used a Metagross and am morally opposed to Mega Evolution, but okay.