Your project is also interesting. I don't plan on ever adding write support. The old Python version was already using git as a library via gitpython, instead of shelling out via the command line. The new version will use Rust's gix.
Performance, even for the old Python version, was pretty decent. That probably came from using git via a library and being careful about fuse caching. I used the 'low level' API that libfuse provided, instead of the 'high level' one. The old version also already supported opening arbitrary commits, tags and branches, they were represented as different folders.
Another feature that's maybe important for performance: because everything was read-only, operations like OpenFile could be implemented as no-ops in such a way that the kernel doesn't even send us a request anymore.
(It was read-only in the sense that any changes would come from the git side. User initiated file system operations could not make any changes to the data.)
