I hear this a lot, and I still don't really get it - git is already decentralized! And not just federated, but truly decentralized where everyone has their own copy of the data. An issue tracker built on top of the git protocol, where issues/PRs/whatever arbitrary other rich text content you want lives inside the .git directory alongside the source code would be much more in the spirit of git. And you could build a pretty modern web interface on top of that!