Player Generated Content
What would you like to see if World of Warcraft added a sandbox creation tool?
I don't know if any of you played City of Heroes back in the day -- it shut down ten years ago, my God, I am literally aging to dust like that one villain in Indiana Jones and the Last Crusade -- but one of the elements it had that fascinates me is that it had a content creator added at one point, where players could create small adventures for other players to experience.