But Swift solves a lot of the problems while having superior interoperability with Objective-C. Rewriting ObjC code to Swift code is relatively easy. Rewriting Objective-C code to Rust would be a massive undertaking I highly doubt would be worth it. Rust and ObjC have too different ABI and are conceptually too different to make bridging the languages easy.

I have seen these attempts in the past with C++, Python, Ruby etc. it never worked well. Apple only succeeded when they made a language specifically designed to interop well with Objective-C.

It is far more sensible to evolve Swift than to adopt Rust. Rust is anyway a niche language. Swift has a much broader appeal. You can teach most developers Swift in a reasonable time.