I suspect this would be most useful in working around 2.6/2.7/3.1 differences and loading different files/polyfills in response, or something. But old versions

I suspect this would be most useful in working around 2.6/2.7/3.1 differences and loading different files/polyfills in response, or something. But old versions arn't going to magically retroactively implement a new PEP, so we won't see the benefit for some time. Other than that it's hard to imagine a use case for needing this sort of information.