Like Manaphy in OU, Hoopa-Unbound has a plethora of coverage moves it can run, all of which allow it to bypass most of its checks on any given team. It can't run all the moves it would theoretically have to, yes, but if running the right ones in a given matchup, it can still wallbreak with ease.
Know that I'm not so much pushing for a high viability ranking or anything like that, I'm just pointing out the potential in theorymon that I see with this mon. It's undoubtedly a wallbreaker, and I can see a set of Hyperspace Fury / Gunk Shot / Grass Knot / Filler performing decently with Life Orb, Choice Scarf or even no item all, for fun shenanigans said in my last post. It has issues getting in, but there are ways around that (slow U-turns, revenge killing, double switching, TRICK ROOM, etc. etc). On the Trick Room bit, it's something I've been playing around with since the beginning of this generation, but haven't quite been able to build a good team around yet, and this mon is absolutely made all the better by it. Diancie, Bronzong, Dialga and/or Gothitelle (lol hoopa-ub + gothitelle = fuck stall) are all very viable TR setters, and can set it up on many common threats in this meta.
tl;dr I'm not calling it an S-rank mon by any means. The original question asked was simply if it would have an impact on the metagame, to which the answer is more than likely a yes, and definitely from myself. Any opposing points can be gotten across by pointing the gun at the post, not the person who made it...