I have had this idea for Quit some time but I do not have the time or the editor knowledge to make it happen.
I was thinking about a map (the largest size available)that had a central walled off base with air defence all around(theme could be urban,wasteland, etc. really doesn't matter), one or two entrances both with enough defences to prevent an endless wave of zombies/zerglings to push through, so bunkers, turrets, SCV's for repairs and supply depots being used as a gate system,also a ludicrous amount of minerals inside. The idea is that it could be left alone and the base would sustain itself. I'm thinking it would mainly be a single player sandbox map. Something that you could literally leave running and come back to like a screensaver. But the idea of possibly having quests/Objectives to maybe leave the "fortress" to go accomplish with an airdropped team sounds cool as well :P Personally I only have the "Wings of liberty" Campaigns because I only enjoy playing Terran, single player and custom games.