While I think the libgit2 initiative is fantastic, I don't think there needs to be just one Git implementation.

One of my favourite things about git is that the underlying storage and protocol is really simple and straight-forward to implement. You could do a lot of it in shell scripts, if you wanted to.

The stateless storage is simple and consistent, but the thing that does vary is the various operating algorithms: diff, merge, garbage collection, etc.

This creates a really interesting ecosystem where you could potentially have third-party tools that have some secret sauce producing more efficient diffs or fewer conflicting merges but still base it entirely on the open git ecosystem and remain completely backwards-compatible with all the other tooling.