http://forums.xonotic.org/showthread.php?tid=5158
Morphed (AFAIK the guy who did the models in the Overkill mod) is offering a really cheap rate to do some single-player enemy models for an invasion and/or SP mode in Xonotic.
Sounds like a worthy cause to support, and it will hopefully bring some new players to Xonotic if there is a more noobie friendly game mode for it.
Pledge some funds in the thread on the Xonotic boards to get things started. The code for the invasion mode (and also one that is similar to a FPS dota) exists already and is quite fun.