> In my opinion, anyone wanting to deal with low-level details like
> mtimes and modes is probably not using shutil

As a moderately experienced UNIX user, I would say that file permissions are not low-level details.  I see shutil functions as convenient wrappers to automate looping and calling a function, but I do care about file permissions.

If people are still interested in this modification, I think it would need a backward-compatible change, for example in the form of a new argument ignore_permission_errors, or a more generic onerror callback like rmtree has.