the roots ype blower becomes a restriction after the turbo really gets going.

If it was really to work well you'd probably want to bypass the supercharger after the turbo spools up. The roots blower in this case would have to be mounted in the front of the engine and piped to the throttle body instead of mounted in the intake manifold. But then you have no room for a turbo setup. Waste of time but it is kinda interesting from an engineering standpoint.