This is all fine for personal/proprietary purposes, but open source can't be that cutting edge. While type annotations are probably fine (3.5), f-strings (3.6) or dataclasses (3.7) won't make it to mainstream OSS anytime soon. But they are great features nonetheless.
I mean, RHEL 8 is shipping with Python 3.6 and Python 2.7 available. There is no standard /usr/bin/python without making the symlink manually, and the system uses its own internal python for dependent tooling, so it doesn’t conflict with user installed versions.
And, based on my experience, general open source is usually much more cutting edge than the larger distros, that’s the whole point.