Mailman 3.0 was released!
https://mail.python.org/pipermail/mailman-announce/2015-April/000210.html
See Sumanah's writeup of what is new: https://lwn.net/Articles/638090/
It's awesome, we should upgrade. That's all I got.
If there are blockers they should be identified and filed as subtasks/blockers of this.