In another post, Vaneras notes that Protection Warriors are going to be given more ability to do other things than tank, essentially in return for other Warrior specs and other tank classes having their tanking ability raised. Prot should be doing more damage now, to let these Warriors do dailies, solo, off-tank, and in general be competent at things besides main tanking. This will be done largely by putting lots of Strength and possibly other damage stats on tanking plate. The damage should be probably less than Fury, Vaneras notes, but you can certainly expect more than is the case now. Adding Strength to tanking gear will also alleviate some of the pressure when trying to choose between mitigation and threat, since it's more likely that one piece will serve both purposes.
All of these things make me very happy and very optimistic for tanks in Wrath. Tanking will be more fun, spec requirements for "normal" tanking will not be as rigid, tanking gear will have damage stats as well, and all four classes will be able to MT raids. At this point, the old question of "what's the point of being a Warrior" rears its head; Warriors are traditionally the best MT, and Ghostcrawler said flat-out this is not what is intended to be the case in WotLK. Yes, this might knock some Warriors down a peg, but ultimately I think it's necessary for game balance. You don't have a best DPSer or a best healer any more either; having one best tank class is an unnecessary relic that's hindering the progress of the game as a whole. And as mentioned, Prot warriors will be getting significantly more DPS in return. They're basically going to be in the position that Priests now hold in the healing world: the most versatile tank, with the most panic buttons, but not a better tank than the other three classes. That's the way it should always have been.
This is not to say that tanking classes should be totally homogenized. Blizzard is treading a fine line with respect to homogenization already, by trying to build every class up to the same level of usefulness, and also in the world of itemization with the spell power stat, not to mention hit/crit/haste now working both for melee and for spells. The new idea, at least as far as tanks, is for the classes to have different flavors, but the same level of usefulness. For example, look at Feral Druids vs. Protection Warriors in the game currently. Ferals have less mitigation, so they take more damage, but they also have a larger health pool, so they can soak up the hits. As a healer, it may take more mana to heal a Feral tank, because more hit points will need to be healed for each point of damage incoming, but it's also somewhat less nerve-wracking when they take that 7k spike.
Again, healers have a similar situation. Us Priests may have a somewhat easier time than Druids at patching up a spike fast, but Druids have amazing efficiency, and their army of HoTs brings pro-active healing ability that we just can't match. You can bring just about any healer to a five-man, or any sufficient number of healers to a raid, regardless of class, and assuming they've got reasonable gear, you'll probably be fine (especially now that Druids are getting a proper res in Wrath). There's no reason it shouldn't be the same for tanks.