It's just too soon to know, but things like Critical Block and talent that resets the timer on your shield slam should help in both the mitigation and threat area. Warriors will always be the baseline tank from which Blizzard bases all other tanks. I wouldn't worry about Paladins. Until we get something akin to Shield Wall, Thunderclap and Last Stand, Warriors have little to worry about. Now Druids did get some of those tools, I'd be more worried about them.
Also, keep in mind the 10 man raids are being designed around 1 tank, so it would make sense that all 4 tanks are able to fulfill the tank role in that arena.