For example, for a time OpenBSD was trying to switch to pcc, a super simple C compiler so they could get off gcc. They eventually went with clang instead, which is not simple, but presumably the cost of using an alternative to gcc or clang was too high.

It was also written 3 or so years ago, so hopefully rust has improved.

I think they already have enough trouble with Rust in the ports tree that they don't want the same thing in base.