In this thread on the official forums (don't worry, it's not that bad) one of the tanks (Adamas) posted that for their Hard-mode kill, they used one druid - and that the druid in question solo-tanked Thorim on hard mode to 14 stacks and had 56k HP.
The druid in question is Sudhir, who you can check out here. They probably don't have their max stam setup on right this instant, so don't worry about it.
The 56k health is nice, but the big problem with Thorim isn't the high health requirement, it's dealing with Unbalancing strike. Being crittable is no fun, especially when the attacks are coming every .5 seconds and are hitting for 14k+ a hit on normally armored bears. How is he solving this?
Well, for starters, I suspect he's crittable. That's not as horrible as you might think; if the healers know that you're the only tank that's going to take big damage, spam healing someone through 25k hits is not the worst thing in the world. But my gut feeling is that while he's crittable, he's using PvP gear to deal with some of this.
But what if we use enough PvP gear to completely remove crits from the equation, even with unbalancing strike? We may still get crushed, but the crits will be gone - and they're the real danger.
First off, what you need: with 6% crit removal from Survival of the Fittest, Thorim's ability puts you 7.6% in the hole. That means you need a total of 623 resilience or similar defense to deal with this. The easy way to figure this out is with Rawr; you need a total of -8% crit reduction in Rawr in order to be safe from Thorim.
How does this gear look? Well, I decided to not go after any Furious gear. Why? Because deadly gear requires no rating requirement in any slot, and it can be bought via conquest badges if you are so inclined. Plus you get two chances to get it - from Emalon 10-man and Archavon 25-man. I am using JC and Leatherworking; JC really helps, but it's not a requirement. And (this is the important bit) I'm not using a single Ulduar-level item. If you have them, this will only be easier.
Head Deadly Gladiator's Dragonhide Helm
Neck Boundless Ambition
Shoulders Deadly Gladiator's Dragonhide Spaulders
Chest Polar Vest
Waist Titan-forged Belt of Triumph
Legs Deadly Gladiator's Dragonhide Legguards
Feet Polar Boots
Wrist Deadly Gladiator's Armwraps of Triumph
Hands Deadly Gladiator's Dragonhide Gloves
Finger1 Hateful Gladiator's Band of Triumph
Finger2 Deadly Gladiator's Band of Ascendancy
Trinket1 Figurine - Monarch Crab
Trinket2 Essence of Gossamer
Back Deadly Gladiator's Cloak of Triumph
MainHand Origin of Nightmares
Ranged Idol of Terror
Avoidance PreDR: 52.064%
Avoidance PostDR: 47.142%
Total Mitigation: 84.931%
Damage Taken: 15.069%
Savage Defense: 77.388% ~ 1586
Chance to be Crit: -8.055%
So just under 51k health, can't be crit, just a bit less than 50% dodge. Not too shabby. And again - this is pretty much bottom of the barrel. If you have access to Furious gear, it becomes a bit easier (and you get a lot more stamina).
Would I do this? No. It's not that hard of a hard mode anyway, and if you don't already have the deadly gear it's probably not worth grinding for it. (If you have the furious gear or want to get it, that's another story). The amount of resilience gems used makes a lot of this stuff pretty unusable anywhere else; I tried to make the gemming such that only the PvP gear is using the resilience gems, but it's still annoying.
But if you're bored or interested in trying something new, I'd recommend it. I'd also recommend throwing on resilience gear for this fight if you have it anyway (and it's comparable in the slot you're replacing). Having less of a chance to take crits even when you're swapping can really make a difference.