Ok, well, I just had an idea for what the Arthas battle in WotLK will be like, and I want to share it with you. Keep in mind this is not true, and will most likely not be implemented, just an idea. Here goes:
In WotLK the final boss battle will be Arthas, so this is what I think the fight will be like. Around his throne there will be a bunch of undead corpses, this isn't talked about till later though. Now, at the sight of humans, orcs, people, Arthas will start trying to break free of his bond with Ner'Zul (spelling), now in the fight, he will be yelling and he will be extremely hard. Then, when you get him to 25% or something, he starts fighting Ner'Zul's influence on him. Now, he is not in control, but he manages to make himself drop Frostmourne. Now, the tank or someone will pick it up. Now, he will be teleported into a small room, where Ner'Zul is. Ner'Zul will begin attacking the person with Frostmourne. He will be yelling about how, alone, you can't stop him, even with Frostmourne, then Arthas the human appears and is like "I feel remorese for what I have done, and I wish to repent. You do not fight alone!" then he starts attacking Ner'zul, then, all the corpses turn into the human innocents they once were, and start attacking Ner'Zul too. Now, when Ner'Zul gets to about, 50%, it will say in orange text "Ner'Zul's magical barriers are destroyed, he is released!" then they get teleported back with everyone else, who then starts fighting a fully healed Ner'Zul, and it too will be hard, but one of them will have Frostmourne, so its easier. Then, when Ner'Zul dies, he starts yelling like "No! This cannot be! We had a deal Arthas!" Then he fades into Oblivion. Now, when he dies, in more Orange Text it says "When the essence of the blade was destroyed, Frostmourne snaps in half, powerless." Then a dragon of some sort will appear and be like "Yes, Ner'Zul ultimately destroyed himself when locking his soul in the blade, for only his on spirit could destroy him. The Lich King is no more. Then you get your phat lootz and it ends. It certainly wont be tank and spank, also, while the tank gets ported into Arthas's mind, the group has to finish Arthas, and when he gets to like 5 or 10%, he'll restore his health, by like 50%
, so it involves everyone.
Hope you enjoyed this theorycraft, sorry for the wall of text.