That's more of a reason why it's hard to change the core MM/page cache/etc logic, as you have to change all the users of it (every filesystem, etc). Ripping ou

That's more of a reason why it's hard to change the core MM/page cache/etc logic, as you have to change all the users of it (every filesystem, etc). Ripping out a filesystem is, technically, near-trivial. The downsides are fully human: the Linux kernel-userspace ABI is normally considered a golden promise that shall not be broken. The developers don't want users to have a bad morning on which their old filesystems no longer work.