I felt like if I installed Python 3 I'd still need Python 2 around. Didn't have a solid setup for supporting both and still being able to use virtualenvwrapper et al. I think I can just wrap some aliases like mkvirtualenv2.7 and mkvirtualenv3.3. Any better ideas are welcome.
How about pyenv (not to be confused with pyvenv), and pyenv-virtualenv? They are designed for solving this problem.
The decision seems reasonable to me. One could use virtualenv (included in the VM) to spin up a virtual python 3 environment when necessary.
virtualenv (for python3) requires python3 already installed, so virtualenv solves nothing in this scenario.