I haven't personally looked into the Rust based OS (I know it exists), but I can guarantee that they're using inline assembly, fighting with language features,

I haven't personally looked into the Rust based OS (I know it exists), but I can guarantee that they're using inline assembly, fighting with language features, working around limitations, and forgoing safety. I'd be shocked if that isn't the case. I'm not saying that you can't build an OS in Rust or other languages, just that OS development is complicated enough without having to fight your language.