My main problem with the Fairy type is that there aren't many I find worth using (well, besides the obviously Uber Xerneas.) Lots of the Fairy type Pokemon introduced are not good enough to hold their own in OU. Sylveon is probably the best of Gen VI Fairies, and while it is certainly a solid Pokemon, all it really has going for it is a Dragon immunity. Mega Mawile and Mega Gardevoir take up a spot that might be better used with another Mega, such as Tyranitar, Lucario, or Scizor. Togekiss and Azumarill are probably going to be the main Fairy types, but would those two be enough to create a serious decline in the use of Dragons? Especially when they have to face things like the aforementioned Mega Scizor and Mega Lucario, along with other oldies of Steel. It means Dragons can't use Outrage all willy nilly, but they Special Dragons shouldn't be hurt much by this.
In the lower tiers, Fairies shouldn't be making much of a difference since we don't see many Dragons. Then again, we also don't see many Steel types or Poison types, so they might find a place in UU, RU, or NU. I just don't think they will dominate the tier though.
I think Dragonite and Salamence have the moves they need to weather the storm. The other Dragons I see getting a decline in usage, although I only see Hydreigon and Kyurem dropping down to UU.