This is a nice idea, let me ask you a question:

One of the more interesting projects now a days is ForgeFed (https://github.com/forgefed/forgefed) which would allow for projects to use ActivityPub for pull requests, forking, etc.

This is important because so much of the value add of Github isn't in the git hosting (which one can do with Gitea or Gitlab) but in the collaboration.

This is also important because many Github extensions work through their API to glue functionality such as test suites and linting through monitoring a PR.

So where might your project fit in there?