Over the years I've come to the conclusion that all these UIs on top of Git make little sense. Git itself is already distributed, which goes beyond federation. Exposing a Git repo over the network is trivial with HTTP or SSH. It supports code review workflows via email, though I really like the approach of storing reviews inside the repo itself via something like git-appraise[1]. Integrating it with CI/CD pipelines _can_ be simple, if the pipeline can be triggered by pushes.
Instead we've created these centralized UIs over Git, and are trying to get them to integrate with one another. This seems backwards to me since Git is already decentralized.