One thing I’ve never understood about “kernel never breaks user space”.. doesn’t that completely atrophy the kernel, preventing it from ever having big rewrites or architectural changes? What if an initial implantation was terrible, and there are 100x performance improvements to be had by doing a breaking change?
Implement a new API for the better route, isolate the terrible code as much as possible, notify the users, deprecate it, and remove it or move it to a userspace shim after enough years had past and almost everyone was off it?