Dear god this thing looks like a nightmare for stall to face. Something I immediately noticed is its access to
Taunt, Thunder Wave, and Destiny Bond.
With Taunt, this thing can reliably hamper stall. Combined with the power this thing brings, and you've got yourself a seriously potent Stallbreaker. If you look further into Hoopa as a stall breaker, it actually becomes MORE fearsome. Let's not forget how devastating a base 150 SpA Modest STAB Shadow Ball can be. FINALLY we have a mon with the ability to abuse
Magician. Stealing items from Stall mons is pretty damn cruel, especially if it's Eviolite. Add on to that set
Trick, giving things an Eviolite in exchange for Leftovers.
Chansey just a TAD too bulky for you? BAM not anymore
252+ SpA Hoopa Psyshock vs. 4 HP / 252+ Def Chansey: 319-376 (49.6 - 58.5%) -- 98.8% chance to 2HKO
Also, stealing 6% of recovery per turn is nothing to scoff at.
As I mentioned earlier, Hoopa gets Thunder Wave. With it, it's capable of crippling members of the opposing team that want to switch in. Thunder Wave--in tandem with Destiny Bond--allows you to actually kill Hoopa's checks/counters. Nail em with the Thunder Wave, then D Bond. If it's Bisharp, then it dies to either Focus Blast or its own Sucker Punch.
While Hoopa MAY need support to function (Scratch that, Hoopa is pretty self-sufficient. It's probably just going to be another nuke like Victini.) I can ABSOLUTELY see it functioning to some degree in the OU metagame. Whether or not it gets OU usage is entirely beyond my capacity to speculate, but I wouldn't write this mon off just yet.
EDIT: I'd also like to add on that Magician stealing Life Orb from offensive stuff can SERIOUSLY change the things they're capable of killing.
Double EDIT: This thing actually looks pretty good FOR stall as a Stallbreaker that can check Mega Medicham and Mega Gardevoir (See Victini). After the battle with
Smog Frog , I've noticed that this thing (should you choose to go No Item) can shut down both the VenuTran and the SkarmChans cores. By removing Heatran's Leftovers, it allows it to be worn down; Taunting Skarm kills it; Chansey and Venusaur are self explanatory.