Earlier quoted context omitted.
For the local copy yeah but if you want the functionality of gitlab/hub to make a MR online from a fork then you need your own fork tracking the upstream which requires the two copies of the repos, hosted on each of the instances, to know about each other. Otherwise what is the point of having two instances, you would have a gerrit-like system where this is one server and you simply checkout a branch and then make a…
I imagine that creating a fork on your own instance, you just provide a url. UX-wise it isn’t as powerful as the one-click fork of a centralised platform, and I think we’d need a browser plug-in because of the missing implicit assumption of where to fork it.
I guess mastadon has better solutions for this, having existed much longer with federation, but it's definitely a downside. Maybe it's something that can be built into a browser in a more general way the way "email with" is for email links - a list of "these domains are actually federated" and "my options for opening them are" list, and you get links as needed, or popups. But there are additional issues when the post ids don't match on the different instances, so such a thing is not so simple as replacing the domain with %s in the right places.