I was thinking it would be cool to have a single player for Gen. Not an actual set of missions, just a bot ladder like vQ3. You could set it up so you go across different areas fighting the natives (ie fight Doom, Phobos and Crash on mars maps, or go to earth and fight sarge) or you could do other stuff like class vs class TDM or CTF bot matches or something. I don't think it's a high priority addition, but it would give Generations players something to do when there's no one on the servers or their ISP goes down. I don't think it would be too much work, and with a little thought put into it it could be fun.
Addition to the idea- anyone seen the Imp and Arachnotron models? Those could be used as enemies. I was thinking of something like this a while back, as well. Something in the vein of "Hunt."