We've got to the stage now with PEP 646 that we're feeling pretty happy with it. So far though we've mainly been workshopping it in typing-sig, so as PEP 1 requires we're asking for some feedback here too before submitting it to the steering council.

If you have time over the next couple of weeks, please take a look at the current draft and let us know your thoughts: https://www.python.org/dev/peps/pep-0646/ (Note that the final couple of sections are out of date; https://github.com/python/peps/pull/1880 clarifies which grammar changes would be required, now that PEP 637 has been rejected. We also have a second PR in progress at https://github.com/python/peps/pull/1881 clarifying some of the motivation.)

Thanks!

Matthew and Pradeep