Admax88 and I have finally gotten the Classbased mod working with the current SVN code. In order to try it out, you need to be running an SVN build of Nexuiz, along with a recent darkplaces build.
You can grab it here: http://omploader.org/vMXVwMw/nexuiz-classbased-test.pk3
Source code is included in the pk3, but you can also browse through it here:
http://github.com/psychcf/nexuiz-classbased/
So far, just the class system have been implemented, so we can force different classes to spawn with different health levels, ammunition levels, models, and weapons. We still have to get the special weapons in there, as well as the other things (like deployables, etc).
Since this isn't a 100% finished mod yet, I haven't put up a test server. For now, you can try it out by creating a local game.
To do this, go to the server list, hit 'create', and then click on the mutators button. Then, check 'Classbased Gameplay', and close that dialog. Then, choose any team-based gamemode, and then hit start. We still need to get it so that bots choose different classes, but it'll come in time.