I'm a bit worried that Contests will be too Mega-centred, with Mega Evolution not being available for every Pokémon. I liked the fact that even NFE's could compete with Pseudo-legendaries in a fair fight, as a Pokémon's movepool was it's sole defining quality in Contests. But maybe the Mega boost won't be much more than an elaborate combo, as you have to rely on a good timing to get the Judge's attention. Also, Mega Pokémon cannot hold Scarves, so if they can't pull off the Mega Evolution, they will be at disadvantage.
I hope there's a Reset Bag of sorts for Contest stats, so your Pokémon won't be lost if you max it's Sheen with bad Pokéblocks.