Earlier quoted context omitted.
You email the author, the author can merge your patch or pull from your repo/branch. Merging your patch even comes built-in with Git. The place hosting your Git repo doesn't need anything special to support this. You email the author, they merge your patch and then git push.
By this definition, everything is federated, because you can email the author and ask them to post something for you.
Some other federation method through centralized platforms like Github would have to be bolted on to git, email is just the built-in and very much intended method that already exists.