After running through Black Temple after the patch with a Druid, Warrior and Paladin tank, I can honestly say that the "niche" for each is still there. I play a protection warrior, and even though TC, Damage Shield and Shockwave are great crowd control, it still does not replace the awesomeness of paladin consecrate. TC and Shockwave are burst AOE damage, and can initially keep a bunch of mobs on a tank, but loosing mobs to AOE casters is still just as easy. With a palading dropped conscecrate, that effecttive DoT helps keep mobs in their place rather than running off to the casters. Even with Damage Shield adding threat/damage it may not be enough.
Druids also still have their niche, in my opinion. Though armor has been reduced, they normally still have more armor in bear, and therefore mitigate just as effectively, if not somewhat better than warriors and paladins. Frontal crowd control is also nice to see with their swipe, but they suffer from the same drawback as the warrior in keeping multiple targets. AOE damage to mobs infront of them can still cause a change of targets to the casters.
Over all, I think that Blizz has evened the bar on the tanking classes, but still gave them their special area's to focus in. Personally, even in a 5 man, I would still bring a paladin tank to Shattered Halls before I brought a protection warrior (myself) or a druid tank.
"By Grabthar's Hammer... What a savings"