Pokémon Omega Ruby and Pokémon Alpha Sapphire announced

My hope for Stephen is that he collects Mega Pokemon, and that you fight him repeatadly throughout the game like a rival, and in each battle he uses a different Mega Pokemon, before his eventual final battle where he settles for Mega Aggron or Mega Metagross.

That would explain why he has a Mega Charizard.

Didn't CoroCoro says he was learning about Mega Evolution? The Kanto starters+their mega stones were our first real megas(that Lucario doesn't count), could make sense to be his first while learning about megas.