A.I. is useful for this. But it would be even more useful if all new code were written in Rust or some other memory-safe language.

A.I. could also be used to port C/C++ codebases to Rust, which isn't economically feasible at the moment.

AI will have plenty of security bugs left to find in Rust codebases.

I mean I get the sentiment but Rust won't save you against division by zero, it'll just panic at runtime like every other language.

From a security perspective, panic at runtime is not that bad for security. Much better than continuing to run with undefined behavior. If someone sends a malformed video in and it crashes the ffmpeg process you can just log it and restart it. Vs potentially exploiting the system.