CI can definitely done on mailing lists. The interface is bit worse than PRs, but I'm sure with enough imagination that can be overcome.

Pulling local trees has been absolutely better IMO with mailing list. I can literally with single keybinding apply patch to relevant repo, something that takes much longer route with Github. (convert URL to raw.github/whatever, copy and paste to apply, or do clicky-clicky in the Github app or whathaveyou)