I don't think we need a federation of forges. What we need instead is just richer git repos.

Fossil gets 90% there with integrating tickets (issues), forums and wikis as part of the repo itself. When you clone a fossil repo, those are also part of the clone, and can be browsed offline on an airplane. Replies can also be written offline and, permissions willing, synced back up to the remote, either immediately or when the internet connection is regained.

I think this is the direction we should go in, but without hardcoding any specific artifact kind as part of the VCS. Instead, repos should be able to contain apps, which would define policies on what artifacts are acceptable, what rules they must follow, and who's allowed to upload and download them and at what times. The job of the forge would then be to execute those policies and render the artifacts for web users in whatever way the app desires.

With such a setup, moving to a different forge would entail nothing more than pushing the repo there.