In our applications, the callable that you would want to call, that
produces
a Directory, depends on the name that is passed into the _q_lookup.
We don't have that callable available already as a method.
We would need to, one way or another, construct a callable that could
be called with no arguments, but that would still produce the Directory
that we want, the one that depends on the name passed into the
_q_lookup.
This is possible, but I think it makes the _q_lookup (and support
functions)
more difficult to understand.

Maybe there is something different about your url space, though, that
makes
this especially useful.  The _q_traverse functionality was separated
from the
Publisher class in order to give you the power to have it your way.
Maybe
you should give it a try and see how much you like it in practice.