Correct me if I am wrong,but I have not been seeing Cresselia being a fairy type (or fairy/psychic) discussion in the past few pages.It is a VERY likely possibility,as Cresselia is a member of the lunar duo and moonblast is a legitimate fairy-type move.Furthermore,Darkrai causes nightmares,while Cresselia prevents them and dark is the opposite of fairy.
Cress will become the best dragon counter in OU thanks to absolutely monstrous bulk,and it does not need to waste a slot for ice beam and opt for a STAB instead.If it is pure fairy,Latios is the only dragon that will give it minor problems,as it can just trick it a specs (psyshock ain't doin nothin to max/max Cress).Furthermore,it even if it is a psychic/fairy type,it will no longer fear Scizor and Tyranitar(in fact,Tyranitar may be scared of switching in).Levitate grants it the ability to switch in to a +6 Garchomp running the current standard SD set with no worries.
Countering dragons is not all it does,a better defensive typing means that it is a more reliable dual screener,and a better teammate to have in stall teams.Current things that demolish stall teams,like Hydreigon,MixMence,Breloom and SubRoost Kyu-B will be all properly handled by Cress(though it will add a weakness to stallbreaker Crobat,which is not common at all).Getting access to Draining Kiss maybe will be the icing on the cake,because it won't have to rely so much on that semi-unreliable moonlight anymore.A wide distribution of a fairy healing move (like roost) will spell doom for all dragons,and will be a huge boost to Cress.
Overall,I think that Cress will easily crack the top 30 usage statistics in the beginning of the generation,though everything may turn out differently as the generation progresses.