Not sure what you mean by "userland" drivers here, but support for kernel modules written in rust is actively being developed. It's already being used for kernel drivers like the Asahi Linux GPU driver for M1 Macs.
But you can write userspace drivers in any language, as long as that language has basic file I/O and mmap() support. There's nothing special about using Rust for userspace drivers.
PartiallyTyped|2 years ago
https://www.kernel.org/doc/html/v4.18/driver-api/uio-howto.h...
tremon|2 years ago