This seems like the way. Why would Rustaceans bother to "argue their case" before an unwilling board if they can just do the rewrite themselves? Maybe it will succeed, maybe not, but you don't need SQLLite's blessing to test the proposition.
My hunch is that those aren't very serious Rustaceans. Even the original language developers developed Rust to interoperate with C as much as possible, and they often used to discourage the rewrite evangelism. If you are a serious Rustacean, you'd probably be worried about the safety tradeoffs in rewriting in Rust. As your parent commenter points out, a mature C codebase is already tested so well that rewriting it in Rust is likely to introduce more bugs - non-memory-safety bugs that are nevertheless serious enough. That's why I and many other Rustaceans don't recommend it. In fact, some Rustaceans even advise others to not rewrite Fortran 90 code (in order to preserve the performance advantage) and instead recommend integrating it with Rust using FFI.
