In the Pokémon TCG, Mega Evolutions are only compatible with Pokémon-EX cards, which is interesting, because EX cards sort of already did what Mega Evolutions do: they're suped-up, more powerful versions of existing Pokémon, and they're incredibly popular at TCG tournaments. There is a catch to Mega Evolving your Pokémon in the TCG, though. Once you Mega Evolve, your turn ends immediately, so you have to survive into the next round if you want to attack.
In other Pokémon TCG news, the Kalos Starter Set, which features the first TCG Fairy-type pokemon - who are resistant to Darkness-type Pokémon - will be available November 8 of this year. Both the Kalos Starter Set and the XY booster packs will include a code card that will help aspiring trainers build up their virtual deck in Pokémon TCG Online.