I agree with
noobcubed, actually. It's an interesting concept, but things like Mega-Mawile, Mega-Gengar, Mega-Pinsir, Mega-Alakazam, Mega-Gardevoir, Mega-Medicham, Mega-Absol, Mega-Abomasnow and, above all, Mega-Banette would all really work better as a new Pokémon entirely. For things like Mega-Aerodactyl where they threw a few spikes on it it doesn't work as well, but the Pokémon listed above all truly look like they could be brand new Pokémon altogether.
What I don't understand is why Smogon doesn't keep the Mega Stones for a certain Pokémon in OU, allowing the base forms of said Pokémon into the lower tiers...