Note also that the fix you mention in https://github.com/pypa/virtualenv/issues/1704 does not help. You can see that tox does not work even when it uses the latest virtualenv. The bug occurs before that.
The bug simply means that whoever tries to
pip install tox in a venv created by stdlib module
venv on OSX, will invariably run into this issue, scratch their head... google around, and possibly submit yet another bug report (there are plenty variants out there as you already know).
I used to work around this issue by installing tox with an old python2 venv just to avoid this issue... Now I want to get rid of py2 entirely, so I took the time to report this bug (I was already working around it for months...).