Related discussion and background in Issue 10581, although that report seems to be geared at extending the Unicode support even further (disallowing mixed scripts, allowing proper minus signs, full-width characters, Roman numerals, etc).

The existing support is actually documented if you know where to look; see the sixth note under the table at <https://docs.python.org/dev/library/stdtypes.html#typesnumeric>. I agree that the references for each constructor should also document this as well.