Having tanked all 5 man content, Naxx10 and about a third of Uld10 as a frost tank I have the following to bring to this discussion.
Frost is the current Best AoE threat generation spec.
I am beginning to experiment with Blood for boss fights that need more single target threat.
That being said my crit % sits around 12%, so Might of Mograine in 3.2 seems like a useless talent to me.
Blood worms? Great for solo, maybe decent for 5mans, but in the AoE Damage Fest that is raiding in Wrath, they die (I assume) before they do much good.
Will of the Necropolis, with great healers, geared in t7.5+, I regularly spend long stretches of time with incoming damage completely balancing incoming healing, so I may be at 30% or so for an uncomfortably long period of time, that extra damage reduction seems like a good thing.
Death Rune Mastery, Seems pretty pointless if you take improved Death Strike. Those F/U runes make death strikes happen. Even if I have the death runes I am likely to use them to spam deathstrikes.
Dark Conviction/Bloody Vengeance: 12% crit, improving it to 17% isn't worth the six talent points I can use for Scent of Blood Improved Blood Aura, Spell Deflection and other survive more talents.
Improved Icy Touch, used only to start diseases, after that I am death striking with those runes
Morbitity, worth three points because blood AoE threat is so terrible
That being said, here is my tentative blood spec: