I honestly don't know what form an implementation of this would take nor whether the system allows a reasonable solution presently. But... There is a shift towards setup.cfg over setup.py. I am unaware of any way to define command classes in setup.cfg. Maybe something relating to in-tree backends? Though I'm not sure how you nicely compose those for projects with their own. And sure, by the time you include an in-tree backend, perhaps you are losing a chunk of the value of static setup.cfg files.