Another thing is to update mesh stack to more modern language, to improve security and resiliency - projects like B.A.T.M.A.N, Babel, OSLR, FRRouting, etc would largely benefit from being rewritten from pure C to language like Rust.
Why? I mean... we had many "modern languages" that are not "modern" anymore, but the code in C still works, and when rust loses the "language of the week" status, the code in C will continue to be developed, and rust will be like go, ruby and others.
Because of the memory safety, better type system, and better infrastructure of testing. There's even no well-maintained property-based testing framework for C. Rust provides all of this out of the box or with popular crates.
Sure, multiple languages do that and many more will.... will you rewrite all the software ever written to any new language that has something new? The current code works.