Support for shortcuts to submodules (http://git-scm.com/book/en/Git-Tools-Submodules) while browsing the source.

Consider also future mercurial support (STASH-2469) for subrepositories (http://mercurial.selenic.com/wiki/Subrepository)

Github supports this by allowing history browsing to recurse into subrepositories, but I'm guessing a simple hyperlink (parsing repo URL and adding the link as a "virtual" folder in source browsing) would suffice.