Summary

Currently, the minimum versions policy regarding GUI toolkits states

For system or C-dependencies (FreeType, GUI frameworks, LaTeX, Ghostscript, FFmpeg) support as old as practical. These can be difficult to install for end-users and we want to be usable on as many systems as possible. We will bump these on a case-by-case basis.

I believe that in the case of GUI toolkits, this could be amended to something like "If, for a version of a Python binding, upstream doesn't provide wheels compatible with any Python version we support (and still publishes wheels for later versions) and neither anaconda and conda-forge provide packages compatible with any Python version we support, then that version of the binding can be dropped". (Sorry for the terrible formulation.)

In practice, this refers to old PyQt5 versions (#23968 (comment)): clearly, both upstream and anaconda and conda-forge intend to provide wheels/built packages for PyQt5, but the oldest PyQt5 that has a PyPI wheel compatible with Python 3.8 (our oldest supported version) is 5.10.1, and the oldest PyQt5 that has conda packages compatible with Python 3.8 is 5.9.2 (AFAICT). So we should just drop support for PyQt<5.9.2, on the grounds that it is hard to actually test them and that both upstream and conda don't seem to attach an importance to running that version of PyQt with Python 3.8+.

Note that e.g. the wheels part doesn't apply e.g. to PyGObject, which has never (AFAICT) published wheels (so it's neither easier nor harder to test old versions on a non-conda setup).

Thoughts?

Proposed fix

No response