One of the things that nbgrader provides is an “exchange” directory that can be used by an instructor to manage the distribution (1:N) and collection (N:1) of assignments such that only course instructors see the N and individual students don’t see other students’ files.
Is that idea, of an exchange directory, something that might be useful as a generic JupyterHub server plugin that sharing services could then build around?
Offhand, I don’t remember how the nbgallery approach works (I don’t remember if there was a clone button you could use to clone a notebook from a someone else’s account into your own gallery).