io_uring is an improved interface between userspace and the kernel, so it doesn't provide any direct benefits to in-kernel filesystem operations, and the performance benefits io_uring does provide should be largely filesystem-agnostic. That said, some of these recent optimizations may be low enough in the kernel's io stack to also benefit io originating within the kernel itself.

Userspace applications that already have some support for asynchronous disk IO (either through the old libaio APIs or as a cleanly-abstracted thread pool) should be able to switch to using io_uring as their backend without too much trouble, and reap the benefits of async that actually works reliably (if switching from libaio) and with vastly lower overhead (if switching from a thread pool). Databases like PostgreSQL were some of the few applications that attempted to deal with the limitations of libaio, but I'm not sure how close they are to having a production-quality io_uring backend.