The kernel and the C library as a single project

And if it would be a real dynamic library (instead a kernel emulated one), intercepting file system calls would be much easier. Currently libc functions can internally do all kinds of interesting things, but with syscalls being in a separate library they could simply be cought with an LD_PRELOAD...

(And the other alternative for interception, ptrace(), changes signaling semantics and race-free interception of calls in threaded code with ptrace() needs architecture specific code.)