We've used a similar approach to what you suggest in the past. For different webwork courses corresponding to the same class, we've replaced all of the [coursename]/templates directories with symbolic links to the templates directory of the coordinator's webwork course. This way the coordinator could edit a pg file in a single location and all classes would have immediate access to it. It also meant that the prof could create a set in his course, and export it to a .def file, whence it could be immediately imported into other sections without doing any file copying. The problem that arose is that someone still had to go into every other webwork course and import the set. To simplify this, I've created a new Instructor Tool for copying sets from a single course to a predefined group of courses.
Code and a few more details are available at:
I welcome feedback on whether this is a useful feature to pursue.