The SC has chosen to accept PEP 387! https://www.python.org/dev/peps/pep-0387/

On Fri, Jun 12, 2020 at 2:44 PM Brett Cannon <brett@python.org> wrote:
Started at a discussion at https://discuss.python.org/t/pep-387-backwards-compatibilty-policy/4421 to try to finally resolve this PEP and our backwards compatibility policy.