GNU coreutils already has tons of Linux-specific code. But it would be a bit of a kernel fail if io_uring were faster or other preferable to copy_file_range for cp (at least for files that do not have holes).
On a hard disk, copying multiple files in parallel is likely to make the copy run slower because it spends more time seeking back and forth between the files (except for small files). Perhaps that isn't a problem with SSDs? It seems like you'd still end up with the data from the different files interleaved in the erase blocks currently being written instead of contiguous, which seems like it would slow down all subsequent reads of those files (unless they're less than a page in size).
> On a hard disk, copying multiple files in parallel is likely to make the copy run slower because it spends more time seeking back and forth between the files (except for small files).
Certainly not; it's likely to make it run faster, since you can use the elevator algorithm more efficiently instead of seeking back and forth between the files. You can easily measure this yourself by using comparing wcp, which uses io_uring, and GNU cp (remember to empty the cache between each run).