OpenBSD doesn't have a Rust compiler in their core system. Having a core utility written in a language that isn't buildable with tools in their core system is a non-starter.

Once they have their own Rust compiler, or are able to import a Rust compiler that supports OpenBSD to the point where bugs on that platform are release-blockers for that compiler, and which is suitably licensed, they should be able to start (re-)writing core tools in Rust.