I know git doesn't do this by itself, but then we're not talking about github vs raw git - perhaps that's where you're confused by what I'm saying.

All these other services have what you're talking about, and the only cross-repo/org work I can see here is:

* Aligned accounts (person X on one service is person Y on github), if you want that continuity across services

* Forking

And the whole forking/branching/merging side is handled by raw git.

That's why I've been asking what githubs huge centralisation gets us. It has a UI and features that are useful, great, those exist in other projects too, so what is the stickiness?