There's a pretty long thread going on in the General Forums right now that makes an interesting request of the dev team: Let us lose. The argument goes that we've been sort of steamrolling our way through massive challenges and insurmountable odds pretty much the whole raid game, and it's just getting boring. Nothing feels like a threat anymore. We know we're going to defeat it and move on. We need to shake things up.
The more I think about it, the more I like it. Why not let us be on the losing side, at least for a few patches? The Lich King himself could use a bit of help in that vein, for sure. The early leveling game did manage to conjure up a few heart-stopping moments where Arthas "let us win," but when it was time to take that to the next level, it seems like Blizzard's sort of backed off and gone stale. Now, we're holding a Ren Faire on his front lawn while his scourge mostly mills around aimlessly and doesn't make more than a token attempt to do anything threatening.
There would be no quicker way to get him to burst back on the scene by having him or one of his lieutenants deal us a devastating blow, one which we will find it hard to recover from.