Just to contribute a litle brainstorming....
- Remember that git refs only point to one end of a commit chain. The origin is kind of implicit. If bug IDs correspond to *changes*, especially ones that you want to mix and match rebasing, is this a job for StGit or quilt or something else that tracks patches rather than states? - If you do use core git to label bits of development history, are the labels supposed to be mutable heads or mostly frozen tags? - Assuming they're tags, do you need them to be part of the root set for garbage collection purposes? Or do you assume they are already referenced by the development history, and the bug ID links are symlinks that moight be broken if the patch isn't merged?
I really should look at StGit more, because from my current position of ignorance, it looks like possibly a better match to the problem. The main problems I see are that its patches are per-branch, not global, and there's no fetch/push mechanism for sharing them.
Also, you might want to have a "patch" with a single name be a patch SERIES, which I don't think StGit does.