Is it really helpful to have different components of the same project in separate repositories? Are they really that independent? Four independent components for a single window manager seems a bit high to me.

Regarding modularization, I tend to prefer Fowler's criterium that a component should contain code which is usually changed together. So, if you have one component where 95% change slowly and 5% change often, you should split it. However, if you have two components that you almost always have to change at the same time, you should merge them.