There are definitely categories of code where you could realistically expect lift-and-shift from C which you're confident is correct to safe Rust that's maybe not very idiomatic but understandable.

I believe Microsoft has a tool which did this for some bit twiddling crypto code. They have high confidence their C crypto code is correct, they run a process, they get safe Rust, and so their confidence transfers but now it's safe Rust so it just works in Rust software and you get all their existing confidence.

But it's never going to be all code, and it might well never be most code.