I play wow with some irl mates and one problem we have is none of us are tanks.
So we started runing heroics without tank, and actually its not any slower then with thank with the right clasess.
As a frost mage i alone can solo most mob packs in heroics, though it would take some time , and partially due to OP buffs many mobs have which can be spellstolen.
Mirror image is awsome for tanking bosses since with deep freeze cold snap deep freeze you get a shit ton of aggro and then when you pop mirrors it get split and mirrors keep aggro long enough to kill the boss.
Also Rogues can be amazing tanks and ive had Rogue tank clears as fast as real tank clears.
Never really tried it but probably plate dps speccs, or maybe demo locks and BM hunters would be nice tanks too?
Its just that im kinda tired of 10 min dungeon ques and spoiled bitchy tanks, so i say think outside of the box, with such faceroll conent you dont really need tanks.