1. buffed dodge/parry stats: no shield means 20-30% avoidance lost and since DK's will likely not get huge stam pools or armor like druids they will need talents to maximize this.
2. Their tanking tree might contain a huge buff to their stam ala the paladin 26% stamina bonus with kings up. This would still have to be coupled with some sort of heightened parry/dodge build.
3. their tanking summons will somehow benefit their armor/ defensive stats like a bone shield of sorts.
4. Their tanking tree will NOT be their dps tree, for obvious reasons.