Would be very nice to add this feature, increases the scene recognition by the brain by adding extra black edges on the elements of the screen - in QW it would be bsp edges and models. Below projects that may help. I know it would require quite a lot work, or maybe even redesign of rendering engine.
http://en.wikipedia.org/wiki/Cel-shaded_animation
http://pages.cs.wisc.edu/~dynerman/projects/q2/
http://q3cellshading.sourceforge.net/
Look at how QMB does it, should port easy to ezQuake in gl_rmain.c