> I'd love it if we could make this happen for Python 3.11. What can I do to help, e.g. would it be helpful if I drafted a PEP?

A PEP isn't necessarily required right now as https://discuss.python.org/t/how-do-we-want-to-manage-additions-removals-to-the-stdlib/10681 needs to be resolved by the steering council first (it's on our agenda).

> Several projects have switched to using tomli (https://github.com/hukkin/tomli), which is fully compatible with TOML v1.0.0 and is maybe 800 LoC with claimed 100% branch coverage.

Part of the issue with tomli is how new it is; https://pypi.org/project/tomli/#history shows it is only 6 months old and we typically require a project be at least a year old before we consider pulling it in.

If you want to help you could ask the author of tomli what they think about it being added to the stdlib and whether they support that idea.