Rust performed 3x slower and hacking around the language made it somewhat of a mess [1]. Much like Singularity, this is hardly a success story. Although Singularity was interesting from a research perspective nobody doubted that an OS could be written in Rust.

https://scialex.github.io/reenix.pdf

That paper is very old, before Rust 1.0. There was also a lot of discussions about ways that they could have used Rust better at the time, IIRC.

Today, there is no reason Rust should ever be 3x slower, especially in an OSdev context, where you currently have to use nightly.