What's the point of trying to introduce Rust everywhere? Git is a mature piece of software and I doubt a lot of new code needs to be written. Also, Rust is very complex relative to C. If you really need classes, templates, etc, you can stick to C++ 98 and get something that is still clean and understandable relative to recent C++ standards and Rust.
> I doubt a lot of new code needs to be written
I bet someone could have easily said the same thing a year ago or even 5 years ago. It's easy to forget the progress and there are a lot of things happening under the hood that are not obvious to casual users. Just take a look at the git log of the git repository itself. It has a steady rate of close to 100 commits per week for the past year.
That says nothing of potential new features either. There is so much more to unlock in the VCS space, look at new tools like jj for example. Additionally, security landscape is getting more aggressive every day, keeping up with and being proactive against vulnerabilities will be needed more than today.