just like what the title said give the mission making tools to the community with as much complexion as possible i really think that the community will deliver a whole lot of missions that will make the games life span go on for a theoretical non ending time just as i was playing i remembered warcraft 3 and that it has a very very extensive mapmaker (which can make scenarios too) and look what we had from there... a new game ganre (dota2 and LOL and HON) so i really think that if you give the community the right equipments they will have a whole lot of great ideas
i knew about the map editor what i was talking about is missions made by people i dont know if you can make missions with the map editor or not tho