There are two ways to interpret your post. The first is "there's no kernel written in Rust that is as complete as Linux". The second is "Rust is unsuitable for a kernel". The first interpretation is obvious and completely uninteresting; the second is something you haven't supported at all.

People are writing a kernel in rust[0], and a pretty good unix-like at that. I don't like rust, but it's a fine language for that and in general. [0] http://www.redox-os.org/