Good work.
I was looking for something similar to allow this kind of behaviour when dealing with repositories that are created by members of a team (available as a GitHub team/organisation), so that the team repositories, which are forks of the individual project member repositories, can get automatically updated.
We are currently doing this with mirrors, but it may be a good idea to check this approach.
Do you have it in the roadmap? Just checking before forking your repository and implementing this functionality, if easy to do.