If federation really works that well, then it sounds like Mastodon/ActivityPub is ripe for carrying Git repository metadata and discussion. Obviously Git development works very well with mailing lists, other than the centralized server requirement, awkwardness (for most users), and technical limitations of mailing lists. So then you just need your federated discussions to carry patches or point to publicly accessible repos and put some decent UI (of choice) on top of that.

Even issues are mainly just discussions with some metadata attached and as long as they can be surfaced in a way to be attached to a project, then they could be created by anyone.

Hmm.. Surely there is already effort being focused in this direction?