I don't follow this carefully but even I have heard of at least one Rust project that when audited failed miserably. Not because of memory safety but because the programmer had made a bunch of rookie mistakes that senior programmers might be better at.
So in other words, Rust's hype is going to lead to a lot of rewrites and a lot of new software being written in Rust. And much of that software will have simple programming errors that you can do in any language. So we're going to need a whole new wave of audits.
Naturally, she was wearing gloves.
Seeing me, she grabbed the dustpan, threw away her sweepings, put the broom away, and was prepared to now serve me...
Still wearing the same gloves. Apparently magic gloves, for she was confused when I asked her to change them. She'd touched the broom, the dustpan, the floor, stuff in the dustpan, and the garbage. All within 20 seconds of me seeing her.
Proper procedure, understanding processes, are far more effective than a misused tool.
Is rust mildly better than some languages? Maybe.
But it is not a balm for all issues, and as you say, replacing very well maintained codebases might result in suboptimal outcomes.