Huh. I know if I have a server that only has python3, Ansible can configure that server with only the python3 interpreter available. So Ansible can use python3 on the box it's configuring, but not the host it's running from?
I believe they just haven't officially defined Ansible as Python 3 compliant because there are still open issues in Github related to Python 2.
I have been using Ansible exclusively with Python 3 for over a year and only stumbled into incompatible code once, a simple case of string VS bytes literals that got quickly fixed.