I don't have an opinion about the bulk of the proposed change.  But, since _osx_support was mentioned as a model for an _aix_support, I wanted to comment on the history of _osx_support. _osx_support was created as a separate module back when the distutils2 (aka packaging) project was active and it appeared that, at least for some number of releases, both distutils and distutils2 would have to co-exist in the cpython source repo.  So, rather than duplicating the macOS code - most of which had been added on to distutils piecemeal over the years - in both places, we ripped out the existing code from distutils and put it into the new _osx_support module for use by both.  In the end, though, a different direction for distutils was chosen and the distutils2/packaging project code was removed from cpython prior to a formal release.  If we were doing it today, there probably would be no reason to have a separate _osx_support module as nearly all of the code is only called from one place.  Thus, I would not use its existence as a justification for having a separate _aix_support module.