Not sure about predictable URLs, but using git itself for very large repos is maybe not the best idea in general. Everybody will have to clone a 10+Gb repository to contribute even something simple, I'm not sure that's very contributor-friendly either...
Why aren't we just using the redmine facilities at .org? It has the ability to have wiki pages, uploads and a repo if you want.
AFAIK, the redmine file manager doesn't do versioning, which was one of the main requirements.