First I want to say that I dislike binary modules as much as anyone for a variety reasons. However I find the idea of restricting non-GPL modules in a GPL kernel a bit silly. You can not stop someone from using a non-GPL module. The source code of the kernel is available to everyone. It is GPL after all. If someone wants to remove the module restriction, they will. Maybe this is not a trivial task, I haven't checked, but it could be done. They could then release a patch to the world and be perfectly within their rights under the GPL.