I think the biggest issue would be a lack of interfaces to the C side code, they're slowly being fleshed out and each one enables more functionality for the Rust modules.

e.g. the test Ext2 driver a MS dev wrote last year after enough of the filesystem interfaces got hooked up

But even then, I don't think the maintainers would accept one that replaces the existing C driver, that'd break non-Rust builds and architectures, and that's a sure-fire way to get Linus on your case. Best you can hope for is one that complements a C driver, and even then I think you'd need a good reason to have two drivers for the same hardware.