[hoherd]

Rust aside, one thing to consider is that a reimplementation of an existing piece of software does offer the benefit of being able to test the old version and the new version side by side for consistent behavior. You could have an entire class of test cases that is just "do X with the old version, and then do X with the new version, and just make sure the result is the same." There is also the entire bug history of the old version that can be investigated during reimplementation. If the old version has specific tests for each resolved bug, those can also be run against the new version to ensure it has consistent behavior.

In this case though, it's only a partial reimplementation: "Leaving out less commonly used features so as to reduce attack surface", which would complicate that approach.