Renaming distutils to _buildutils only delays the problem to remove it.  But yes, it explicitly makes it explicit that code needs to be changed.

I would like to see that neither distutils or _buildutils is installed by default, and only is available internally for building the extensions of CPython.

The "old" build system to build builtins instead of extensions is still functional, so it should be ok to build the extensions also with the old build system.

That would require moving all the config stuff in setup.py to autoconf tests, which is perfectly doable.  The MacOS and Windows builds would need some attention too, but afaicr when asking Ned Deily and Steve Dower at the language summits, they didn't have a concern about this approach.