> I fail to see what advantage rewriting existing and proven tools with a new language would bring

I think code safety is not an issue here because the Posix tools (and Unix/Linux as a whole) have already proven their extreme reliability.

The only real advantage to rewrite the Posix tools is motivation. A rewrite in a modern language like Rust will likely keep maintainance longer alive than old C code that no one likes to maintain.

It's the same reason why a new display manager (Wayland) is wanted instead of X11. There is basically no technical reason to replace the X server which works very well to this day. However, there are not much people anymore who like to maintain the old X code, or to support new graphics cards in X.