The main complication now is that get_tracker is called before __init__ 
has finished, so a simple implementation that would use a single 
tracker instance (maybe because you know you WSGI server is single-
threaded anyway) doesn't work any more:

class MyRequestDispatcher(RequestDispatcher):
    def __init__(self, home):
        RequestDispatcher.__init__(self, home)
        self._tracker = roundup.instance.open(self.home, not 
self.debug)

    @contextmanager
    def get_tracker(self):
        yield self._tracker