Some of my colleagues did, a few years ago.
The only way I could see a kernel being truly written in Haskell is in a DSL something like atom[1]. Atom is an EDSL represents code that not only doesn't need a garbage collector, but also has a verified constant bound on memory usage. However if that's what you're looking for, you might as well go with an EDSL in a dependently typed language like Idris to make verification easier and extensible.
Redox is a ground up OS, but I wonder if we shouldn't instead be taking more of an Oxidization approach where we rewrite more and more pieces of an existing OS in Rust piecemeal. This would add some overhead (programmatically not instructionwise) of a lot of context switches though between the C and the Rust code, which is to say it would be a little ugly for a while.
It might be cleaner to go after a microkernel to do this though, like L4 or rumprun.
That's kind of the opposite of having the mindshare, IMO :) Having the mindshare means people would be reaching for it when they need things done, not have to be dragged in, and there's a wide pool of people knowing it.
I'm pretty sure you can write OS kernel in almost any language that can be compiled into runnable code, and probably if you are really determined also in those that are compiled into bytecode. As I said, it's not the main issue.
Unless you are a titan of programming that can do an OS project all by yourself, or have more money than Google, you'll need random people to come to the project, pick up pieces and work on them. The question is, does Rust have pool of people wide enough so that probability of people wanting to work on your project is higher than your needs?
C definitely has a huge pool. So do C++, Java, JS, Python and many other languages. Rust? I'm not sure it does so far. Maybe I'm wrong.
I think for its age, the success it already enjoys is impressive.