Why even bother to try to do Icecrown?

Q u o t e:
The loot will all be replaced by quest blues and greens in a little. Im not gonna even waste time to get outdated loot

It's true that things will continue to change in an ever-evolving massively multi-player RPG like World of Warcraft. By your logic though, there's no point in doing anything in the game since a new means of progression will always present itself further down the road. The point is to focus on having fun experiencing the content available to you at any given moment. I say bother to do Icecrown because the Lich King is one of the biggest names out there, plenty of challenging, fun encounters will present themselves, and players have spent this whole expansion working toward getting into the citadel. Key pieces of the epic storyline of the Lich King and the heroes who are working to destroy him will play out in both the dungeon and raid of Icecrown Citadel. Sounds like fun to me, regardless of what is to come in future expansions.