A titlemap cvar for Darkplaces would do great. The cvar would be altered by map's triggers probably for the appropriate map, and the cvar would be saved in the config, and it would be, well, the name of the map you wish to start in during "disconnect" menu startup. Notarget could automatically be enabled in the titlemap. With some clevar QC moving cameras and such, you could create Unreal-style flybys!
Zdoom just got TITLEMAP support too