Those of us that have wasted too much of our lives on these boards for an extended time might remember the old Quest Creation contests. One saw players submit designs for entire quests; the other saw players submit and then vote on, in a series of rounds, little pieces of a quest idea.
Here's a suggestion to Turbine: Run a forum contest where players can create their own quest design. Offer a 2000 point prize to the creator of any quest you actually implement in-game (in a recognisable form). Make clear that there will be between zero and three winners (so if there's no great designs, you don't lock yourself into adding a mediocre quest). Don't ask for full 3D maps (although people can make them reasonably easily in Google Sketchup, which is free), but instead get players to give a basic outline of the maps, foes, non-monster challenges (traps, puzzles, mazes etc), and a compelling storyline for the quest.