Ok, I,ve checked out this forum and apparently the verdict is that dk tanking will be done in a high parry or avoidance fashion. So pardon me but you are very uncreative people. (if that sentence hurt your feelings don't QQ to me about it)
Now I don't know much about the four healing classes in place but I do know druids HoT, shaman have big heals but aren't mana efficient, paladins have small heals that are, and preists do a little of each. So they all cover different situations.
What I know about the tanking classes is that Warriors have the best single target threat, druids do great against melee mobs due to uber high migitation, and paladin's can take many mobs at once. So to say how a dk will be able to tank is irellavant, thats blizzards job to figure out.
What I think tanking a dk will be like from a speculative stand point? Now that is the real question. If you switched dk from the previous question into druid the answer would be by turning into bear. I personally think a dk tank will tank by sucking life from mobs with auras and spells renplenishing a fraction to his party.(so like a shadow priest) But being a tank the damage would be small compared to a shadow priest. Maybe it will be high but a good majority of dk tanking abilities require health to use? Maybe he won't heal at all, but I strongly stand behind a leech-tank for the fourth style of play.