SQLAlchemy's issue repository will remain hosted on Trac;
while a Git repository can be mirrored in any number of
places, an issue repository cannot (for now! Can someone
please create a distributed issue tracker? Should be
pretty doable, though getting Github/Bitbucket to use it,
not so much...), so SQLAlchemy's long history of issue
discussion remains maintained directly by the project.
There are many different projects which implement distributed bug tracking[0], some better than others. The question of how much distributed bug tracking makes sense depends strongly on the structure of the project. If the project is developer heavy (such as developers responding to user help requests) it can work well, but if the project has several strata of developers and support people and users then it might not make as much sense.
