I guess the way Blizzard goes, with DKs as a 4th class able to tank, will be to give every tanking class some sort of viability in "specialized" roles - that we need in 25 man raids - where they really shine over other classes, while every tank will be fully viable in 5man and 10man content.
I think of something like M'uru 2 for example:
Large number of AoE-Mobs for Pally (maybe DK?) tanks, some abilities that must be spellreflected by Warriors, maybe some Mobs with heavy, but low range AoE-Effects that must be tankey by a DK and killed by Ranged-DDs and 1-4 Adds that must die very fast where extreme snapaggro is needed.
edit after reading above post:
Yeah, what about a conversion of Feral AttackPower into armor that gets multiplied by Thick Hide?
