Trust me, GG would not even be playable in Unlimited. Things like Jolteon, Blasticune, and Vileplume ex would overun that deck.
To the OP, the reason Unlimited won't ever be featured in tournaments is because 90% of all games end on Turn 1. Jolteon ex, for instance, can pull off a 60, 80, or even 100 damage spread TURN ONE. Blasitcune has potential to deal 100+ damage on the first turn, and it only gets higher as time goes on...Vileplume ex is Dialga G on crack, locking your Trainers and Stadiums via a Body. Considering Trainers are at LEAST 30% of your deck, and more likely 40-50%, that stings. Good luck setting-up at all without Trainers, as Unlimited decks run few to no Supporters...seeing as they are slow by Unlimited standards. Vileplume ex is not amazing at all in attacking, but Vileplume will end up outstalling you because a good chunk of your deck is now useless...as even dealing 50 (or 40 with DRE) and some Conditions will still end up killing you.
Yeah, you REALLY want these decks in a format? I didn't think so...all of them are pretty much current Modified decks on steroids. =/
EDIT: Ah, I forgot about Mewtwo...however, even he will be torn to bits by Blasticune and Jolteon ex. He could beat Vileplume, though.