https://docs.python.org/3/c-api/unicode.html#deprecated-py-unicode-apis
says "Deprecated since version 3.3, will be removed in version 4.0."
(I am aware that the quote above was written before we decided that '3.9' should be followed by '3.10' rather than '4.0' to avoid giving mis-impressions.)

There is currently no plan for a '4.0' and part of the reason is that it stirs up unnecessary negative feeling in people.  For example:
https://stackoverflow.com/questions/53899931/why-does-an-empty-string-in-python-sometimes-take-up-49-bytes-and-sometimes-51
The second most upvoted comment (9) is "seeing a reference to a "[Python] 4.0" is giving me anxiety..." – Mike Caron (11000+ reputation).  We, as well as they, don't need this.

When '4.0' was used in an asyncio deprecation, it was changed.  Let us do the same elsewhere.