I think that they should do a sort of mod, which you can play any mission, but with the options in multiplayer, like for instance, if I want to play this map, but with the equipments (that you buy like in multiplayer),
Or they could make a sort of defense mission, in which you choose what team you want, and wait for the enemy to attack and all...
You've got the map editor. You can make all of that and more.