You've been told about this before. We don't do "spec reviews" that don't include logs and numbers to back them up. This isn't your blog. Also, you are incorrect on the information on Blood Queen.
I futzed around with Unholy tanking (13/5/53) doing a bunch of 10-man hard modes since I was the only class in the raid that could spec a COE debuff talent and a tank didn't show up. Mitigation wasn't too bad. Notable highlights were:
Blood Queen - being the offtank (blood mirror tank) is great because none of the damage eats Bone Shield charges, so you take 20% less damage for the entire fight plus another 6% less magic damage on top of the frost presence/blade barrier reductions. I took vastly less damage than I did last time I did it as blood. My HP never dipped below 50% at any point during the encounter.
Dreamwalker - a complete joke. 15 second DnD with impurity, near-infinite RP, still able to get 4xIT in a rotation? Could probably solo tank it.
Deathwhisper - Obviously the best spec for adds. Boss threat may be an issue with rune strike being noodle-like, I just blew cooldowns and hit the boss hard in frost presence until I passed the starting tank, then blew ITx4 ERW ITx4 for a 300k threat lead before I got the first stack of the debuff.
Blood prince council - Keleseth never hit me for more than 12k. Had 4/6 nuclei fall off in rapid succession during his empowerment, AMSed and took 0 damage. Running around collecting nuclei / getting knocked back from a bad shock vortex I hit 54 stacks of the debuff at one point and never even noticed since bone shield counts against that too. Bone shield uptime really high. AMZ absorbed almost an entire empowered flame. Really good spec for that fight.
Putricide: I cannot recommend this spec enough. Just pestilence diseases onto every add with glyph of disease and laugh. You'll never have any threat issues since DPS will be on adds half the fight while you build a gigantic threat lead on the boss. Your threat and damage is mobile and keeps ticking while you're knocked back by volatile ooze or kiting, bone shield, 6% reduced spell damage taken, AMZ are amazing for phase 3 when plague is stacked high since putricide's melee is not much of a threat to you. Definitely 25-man HM viable.
Saurfang/Festergut: Sucks. Fast, hard hitting physical bosses, it's definitely squishier than blood unless you're really careful with bone shield usage and cooldown rotations. Bone shield needs to be treated as a 20% for 10 seconds shield wall on such fights. Frenzy with him at 80 BP - Bone shield / BT (proc 4pc T10), leading into an IBF. Snap threat is also sketchy, post-taunt some IT spamming is sometimes required if the other tank is being shield slam happy.
Didn't do lich king. I can see it having some viability on heroic lich king with some group comps but blood will probably still come out ahead with WotN, though you will definitely take less soul reaper damage than a blood tank would if you manage cooldowns properly.
Single target DPS is very very strong. Breaking 4.5-5k (with the 15% buff) is easy, I could see doing 6k in a 25-man raid. Rune strike is definitely not as powerful of a threat move as unholy. Perma-ghoul is specced into mostly due to lack of places to put points otherwise, other tank brought imp thunderclap and I didn't need more threat talents. Gargoyle / ghoul contribute roughly 800-1100 dps for 3 talent points because ghoul/gargoyle derive the largest amount of their damage from your strength, which you will still have a lot of in ICC tank gear.
Permaghoul (if managed properly) will also absorb the first hit a boss deals. Just pull with your pet - have it leap/attack as you run in. The boss will do a 180 to hit it just as you get into melee range, so your first attack on the boss will be to its back meaning you're way less likely to get parried. The boss will also not move from its starting position so you won't need to fumble around moving it back like you would on rotface or blood queen. Warriors and druids have opening gap closers, a perma-ghoul serves part of the same purpose for you in regards to boss positioning. It's also a free ~25k heal if you see yourself get clobbered by something. The pet stun is relatively useless on boss fights but has some utility that can't be overlooked as DKs are the only tank class without any trainable stuns.
Overall I would say unholy is definitely still endgame viable and is definitely vastly better than frost at this time for a lot of fights, frost just has way too much bloat in the tree and no good cooldowns. Blood is "king" but there's a number of fights where unholy will outdo it.