Survival mode we do have maps of this style already, with a single exit.. Forget the name of those. One is particularly good as the exit is a short dig below, but anyone trying to dig for it before killing the others WONT succeed, so it works out.
edit: Yea CCX just posted as I was typing. Hes got the right link to pics haha.
CTF: This would actually be a fantastic addition to Lix, if it could be coded into the game one day, such as you walk over a 'flag' or some new object, and immediately change color(or something else obvious to all) to show the flag carrier. Only a flag carrier can 'exit' as long as their own flag is in its home position.
^ would be crazy to play it with a bunch of Lix! haha