Now that 3D HW is popular, it appears to me that at long last, it may be time to move to full 3D window management. A relatively easy first step might be to use one of the existing 3D object scene managers, and write an X11 screen driver that merely calls OpenGL functions in that scene manager instead of calling the 2D drawing routines.
This isn’t the most efficient way possible, but there are very few primitives in X11 so it would be a good ‘proof of concept’. The result would be the possibility of keeping multiple virtual X displays floating in a 3D space. Thus, the existing X11 window manageres would continue to manage the X screen without knowing the screen is virtual.
Of course, there’s lots of work to follow up, including determining ways to handle the context switches and managing the virtual screens. This could be done with a program that is called with a special keystroke, for starters.
In the long term, an OpenGL display manager has the potential of being smaller and more efficient than X11, and could replace X11 under the open source OS. But it must support legacy X11 apps, and this is the way to do it.