First you have to work around things like direct memory access, writing a "safe" wrapper around direct memory access doesn't really take it from unsafe to safe and you have to fight the language to do the things you have to do when doing kernel work. Then you have to deal with badly optimized output of the compiler which is fine in an user space program but a no-go in a kernel or even worse on embedded. I know some might say "well you aren't supposed to do that, you need X safety measure" but the hardware doesn't work like that, if you try to apply those concepts to out-of-order execution for example you will incur a heavy performance cost.
tl;dr Rust fanboys should read some kernel device driver code and lower level code before giving their input
Ironically you say this on a submitted project that uses Rust for systems programming.
So just like with St. Thomas, apparently we need all those Rewrite in Safe Systems Language XVYZ, to bring the non-belivers into the righteous path.
Which is anyway only half of the battle, as Joe Duffy points out in one of his talks, several developers on the WinDev team dimissed Midori efforts, even with the system running in front of them, providing them wrong in all their remarks about the system.