Psychic dark is a pathetic defensive typing (no resistances), while it's not too bad offensively, basically when your opponent sends in a u-turner (scarf lando, scizor), they're guaranteed to get some momentum back, because hoopa will have to switch out, and then they'll u-turn out into a check or counter.
Why is everyone so hung up over Hoopa's 4x weaknesses. As if it makes a difference if it's 4x or 2x or even 1x. It's about as physically frail as Weavile lol.
252 Atk Landorus-T U-turn vs. 0 HP / 0 Def Hoopa: 254-300 (84.3 - 99.6%). - This is a damage calc as though Hoopa was only 2x weak to U-turn.
252 Atk Landorus-T Earthquake vs. 0 HP / 0 Def Hoopa: 271-321 (90 - 106.6%). - Of course Landorus can simply KO it with a neutral hit anyway.
Same with its normal form. Pursuit and Sucker Punch will OHKO regardless of 2x or 4x. The only relevant Ghost move in OU is Gengar's Shadow Ball and that isn't something that Hoopa should try to fight anyway.
Anyhow Hoopa unbound looks murderous. 160 base attack powering deadly Knock Offs and Drain Punches, 170 base special attack and Nasty Plot makes it completely impossible to switch in on. It loses its Ghost STAB but that's okay because it gets way better replacements in STAB Hyperspace Fury and Knock Off. It has bad physical bulk but it has Latias level special defense and Deoxys level offenses to make up for it. 80 base speed is decent enough to be usable and more than enough to shit all over most walls.
It can run Life Orb, Specs, Band, Scarf, Sub + CM, Sub + Sitrus Berry, Nasty Plot, Assault Vest, and probably a ton of other sets I can't think of. Dark / Psychic lacks resistances but it also lacks weaknesses so it can abuse its titanic special bulk and switch in on things like Zapdos, Gengar, Latias, Venusaur, etc. I don't know how Hoopa Unbound will do in OU but it will undoubtedly find some uses.
If it's ever released anyway.