The goal is to get this is merged into Rust's std library, they wouldn't write std on top of Rustix.
> Wonder if that means it would be easier to verify the correctness of `unsafe` use inside Rust itself?
If you mean usage of unsafe inside std (which the Rust compiler does depend upon), that is one of the explicit goals of Rustix. The usage of unsafe will be much more narrow overall, mostly surrounding the system calls themselves.