Well back in WC3 the dread lord and Arthas had some neat auras that could be incorporated into wow for tanking purposes.
The dread lords vamp aura, perhaps the DK can turn this one on in order to regain life while getting hit by mobs. Blizz could also put in some threat gainer along with hp regen or something.
Arthas's unholy aura gives movement speed and crazy hp regen. Another way to help a DK while being a tank.
I havent read much so im speculating but if blizz wants the dk to be a 2handed tank, but the DK can also dual weild, i assume that 2-handed talents will be throughout the tank tree to increase avoidance and threat %'s
If the DK can really tank while doing decent dps, it could be the end for the current tanks in new 5 man content at least.