I agree with Martin that once we go to git, every project has its own independent repo. That shouldn't take much time at all to do, I can just run some svn2git magic to spit out separate repositories. The question will be where those repositories live. I can host the repositories again. I could replace the tired Trac interface with Gitlab and then host the repositories locally and through there. If that's the case, Github repositories could be forked in Gitlab and/or point to the Github repos? (e.g., for people who only want their code on Github). I think the downside of Gitlab is that it doesn't seem to be very customizable to, for example, have a coherent single Wiki of some sort like Trac dd. It will be a bunch of separate Wikis buried in to each separate repository's page.
So I think we are agreeing so far on git with multiple repositories for each project. What we need to figure out is what the frontend is.