For Unburden sets, do they need to run max speed? I figure you could probably sacrifice some speed for bulk (what little bulk you've got) because Hawlucha already sits at a very nice speed tier. He's still sadly outsped by things like Greninja, Aerodactyl, Jolteon, 'Zam, Noivern and Weavile, but an Unburden boost essentially makes him scarfed without being delegated to one attack. But his immediate speed is still nice so... do people still go for full speed instead?
I feel that if your team has sufficient checks to the aforementioned Pokemon that outspeed Hawlucha, you could use Hawlucha with Limber instead. Unburden is cool as hell and Hawlucha looks like it's poster boy and all, but it's not always necessary. Hawlucha's speed tier lets it do amazing things like revenge many of the Megas without a boost. It's not stopping Mega Pinsir any time soon though (unless you give it that anti-flying berry, but that's situational, and it doesn't help too much against Talonflame either).
I think Hawlucha's supportive options should be further discussed, as this thread has almost been exclusively about the 2 STAB + 2 Misc. sets (though I feel these are the best general Hawlucha sets) and some gimmicky power herb ones, with a bit of Baton Pass here and there.
Hawlucha has some great anti-lead options. It's got access to Encore, Taunt, Baton Pass, as well as plenty of boosting moves. In this regard, it can do a lot of what Mienshao can do, but with better speed. Hawlucha can be tailor made to hard counter dual screen Klefki as well (Limber, Brick Break, Taunt, Encore all make the set of keys wish it was never born) but this is generally a waste of Hawlucha's capabilities.
Let's also discuss the things that generally can get past Hawlucha in OU. Aegislash and Talonflame had been mentioned all throughout the thread (though Talonflame is kind of a shallow check who risks getting KO'd on the switch if rocks are up, so it's better suited to revenging Hawlucha). On the topic of Aegislash, the mixed-attacker sets are definitely ones to watch out for, as there may not even be any mind game shenanigans if they simply fire off Shadow Ball and Shadow Sneak after switching in on anything you did. Though you could run a gimmicky fling set to try and catch it off guard, your best bet is probably just to let someone else handle Aegislash. While you can play games with SD sets, Hawlucha does not want to take any hits from Aegislash really, and shouldn't bother staying in. Though if you really want to try beating Aegislash with Hawlucha, you can attempt to use Me First to hit it with a 1.5x Shadow Ball. Though I doubt this KOs shield form with Hawlucha's univested special attacking stat.
What other things give Hawlucha problems? I can see Landorus-T being a huge thorn in our flying friend's side. Intimidate + resistance to high jump kick means relying on Acrobatics for damage, which Landorus-T can definitely tank. Hawlucha may not be weak to Earthquake or Stone Edge, but some variants of Landorus-T carry hidden power ice, which is not fun to take. Hawlucha CAN itself pack Hidden Power Ice (it's special attack is pretty awful though), but other than Ground/Flying types, you'll probably just want to smack things hard with +2 Acrobatics or something.
I doubt Hawlucha enjoys taking Slowbro head on either, and it would be more prudent to simply U-Turn or Baton Pass out against it, rather than risk Scald burns or simply getting wrecked by Ice Beam/Psyshock. Gliscor can be troubling thanks to it's good defense and similarity to Landorus-T, but since so many people forgo attacking moves other than Earthquake on Gliscor, you may end up being immune to Gliscor just by taunting it.
Hawlucha's pretty hard to switch into, and it can mess up defensive 'mons with Encore, Taunt, and it's plethora of support options. But Hawlucha is pretty easy to revenge kill. While a lot of things are 2HKO'd by +2 Hawlucha, most things can endure that initial hit and finish it off. Scarfers beat Hawlucha if it isn't boosted by unburden, and it can easily be worn down throughout the battle to be picked off by priority somewhere along the line.