There is git-appraise to fill that gap [1]. I am personally waiting for a federated "forge" for federating PRs across platforms, such as the one developed in [2]. Maybe via e-mail? [3].

[1]: https://github.com/google/git-appraise

[2]: https://github.com/forgefed/forgefed

[3]: https://drewdevault.com/2018/07/23/Git-is-already-distribute...