Based on the PEP 617 acceptance thread on python-dev, lib2to3 is eventually going to run into trouble parsing modern syntax a few releases from now.

It would be better off maintained outside of the standard library.  It gets used by a lot of things and is generally useful, but would make a lot more sense as a PyPI project than as something only quasi-maintained within the stdlib (it only gained the ability to parse a couple modern syntax features in via bugfix contributions to the stdlib the past month or two...  meaning a lot of versions of it out there cannot)

Black has already forked it.

goal:  PendingDeprecationWarning and documentation as such in 3.9.  Move to DeprecationWarning in 3.10 or 3.11 and remove it by ~3.12.  Subject to our existing deprecation process guidelines.