I was actually considering doing the same thing after seeing a DDay thread about using paintball2 to play. I'm not sure if it would be better to make it a separate project or make the paintball2 engine support both Quake2 and Paintball2. On one hand, there would be a lot of redundant things having them be different projects, but on the other hand, Paintball2 is moving further and further away from Quake2, so it might be difficult to keep them compatible. The ideal solution would be to make a client side DLL, like some engines have done, and keep it all one project, I think.