we can probably add a section that includes all supported platforms and possibly "partially" supported platforms, and maybe include platforms that currently aren't supported but want/plan to be supported.

We have this: https://pythondev.readthedocs.io/platforms.html

While there's is useful information on that web page, I don't think it is a satisfactory answer to what I believe is being requrested here, namely, "How do I determine to what extent platform X is supported by cPython?"  First, the information on the web pate is somewhat out-of-date. But more importantly, the web page is not part of the official Python documentation or python.org web site. If we are going to better document what we support and in a way that implies some commitment on behalf of the cPython project, it needs to be published under the review and ultimate control of the steering council, like all other official documentation.