The idea is role an alt on a new server (preferably PvP), a race you have never played before, a class you have never played before, and (possibly) a faction you have never played before.
The idea is you start playing and you are now starting from scratch on that realm, sure you won't be as noobish as you once were, but it may bring a fresh and new feeling to the gameplay.
Death Knights are not allowed. You may even try the ironman challenge with it if you like, but not required at all.\
This is mainly an idea to have some fun playing before MoP roles over.