I can't imagine straight fairy (or fairly straight fairy) not becoming a really strong archetype.
M-Gardevoir is just too good and goes too well with the rest of fairy. For people who run fairy and aromatisse already, it's just an automatic inclusion for that 2-2 slot where the mega usually goes. Much as I love M-Manectric the better weakness and the fact you don't need that rainbow energy, that's going to swing it. And then there will be a bunch of people just wanting to take advantage of the card.
I think the steel weakness is not a huge issue. Better to have steel as a weakness than fighting. Right now steel is just not an amazing type, and it doesn't look like the new set will change that. Compared to other top decks, it's probably one of the best weaknesses to have. Yveltal has electricity, which is everywhere. Donphan has water, which is going to be everywhere. Toad has grass, which is the type of one of the top three decks in the format. Manectric has fighting, which is the type of one of the top two decks. Probably only VirGen has as good or better weakness.
Everything else is a bit speculative, but a few things seem possible or even likely
- We're going to see quite a bit more water because of dive ball and rough seas which ought to hurt Donphan
- Stadium wars. There's going to be a lot more stadium wars
- Supporters other than N, Sycamore etc are creeping into the game, and I think that will continue.
One thing I am really hoping for is a new fire archetype. I don't know if the new stadium and Camerupt will be enough... it doesn't seem super-likely, but who knows?