When K&R created unix and C there was still the better option of moving changes that were better to have in the "kernel" into the kernel.
Now we have "standards" that even cause headaches between Linux and BSD's.
Linux back-propagates stuff like mmap, io_uring, etc. to where it belongs. In this way it is like the original unix. And deservedly running on most servers out there.
Rust uutils would be a good place to design a more foolproof replacement for Rust's std::fs API.