Git is already distributed. Maybe there should be a way for forge software like GitLab or GitHub to fork stuff from each other via UI, but you can already do that by cloning and pushing the repo to somewhere else.

Git itself is already distributed. For federated issues/pull requests, there is the ActivityPub extension ForgeFed. Forgejo ist actively working on implementing it.

Both gitlab and gitea/forgejo has plans to add federation. But it’s been planned for years now and I’m not sure how close we are to actually getting it.

Besides, git itself is federated as you create copies of repositories on your computer, just like anyone else. It’s just not very “discoverable”.