In my experience current AI is still far from reasoning about the kind of hard-to-spot bugs in C that lead to the worst exploits. Rust solves most of these by design. It isn't about adding a second language - it is about slowly phasing out a language that is being misused in areas it shouldn't be in.

C will at some point be relegated to being an educational language, incredibly valuable due to few but good abstractions over assembly. It will continue to exist for decades in most systems, but hopefully it won't be used outside of the maintenance of legacy systems.