I'm still waiting for supervisor, beanstalkc, and cloudsigma.
Here are the blocking issues for official support: https://github.com/Supervisor/supervisor/labels/python%203
I've been running it under Python 3 for a while with no problems.
In your case you know exactly what your needs are, and that they're unsupported in Python 3, but I'm sure that many of those 70% Py2 projects could run just as well in Py3.
Can I ask why you're using supervisor instead of systemd at this point?
Systemd on the other hand is just something that is being forced down our throats. :-/