RIIR doesn't scare me at all -- as a user, my experience has been the rust rewrites are usually high-quality improvements over the original. Ripgrep is legendary!

It is a huge accomplishment of Rust to enable the creation of better versions of lang-standing highly-optimized-C tools.

(Which inspired me to kick the tires a bit on the language; it felt like C++ done right to me. Being able to write threaded code w/o fear of data-races is very cool.)