perhaps something of an escalator like quests that start at MP0 level and progresses through to MP10 with gear benefits along the way. might be one idea.
I know that Blizzard would probably prefer to put content into an expansion, but small stuff along the way would mean less people dropping out of the game so when there is an expansion they are in a level state to pick it up not go whats the point I got to level up first before I can play the expansion so I dont think i'll bother.
Oh! also thought someone should shout out for the PVE side of things so its not all PVP sided.