Pagure [0], Fedora's git forge, hosts code, issues, docs, and pull requests as four separate git repositories under the hood [1]. However, only project administrators can clone most of those repos.

[0]: https://pagure.io/pagure

[1]: https://docs.pagure.org/pagure/usage.html

I can imagine that working to a degree: Make a fork of a commit at an issue, then merge that fork back in with master at point of fix. Bit of a mess in the tree though.