I rebased my work on current master of the cpython git repository, cherry picking the changes from the old branch (that was based on a at the time unofficial git mirror of the mercurial repository). 

To avoid any ambiguity I called it "issue22228_3", so it is now available here: https://github.com/lelit/cpython/tree/issue22228_3

Since now I own a Mac, I could find the energies to adapt the changes to libedit, if at all possible. That would be even more likely to happen should I receive some positive feedback on the chances this has to be accepted :-)