IMHO a kernel managing a file (any file) all on its own imposes too many assumptions about hardware and user space. This could unexpectedly bite you if you're i

IMHO a kernel managing a file (any file) all on its own imposes too many assumptions about hardware and user space. This could unexpectedly bite you if you're in a rescue system trying to fsck, booting from external RO media, running diskless or from NFS, etc. Meanwhile Linux allows you to swapon(2) just about anything. A file, a partition, a whole disk, /dev/zram, even a zvol. (The last one could lead to a nasty deadlock, don't do it.) Perhaps the XNU/NeXT/Darwin/OSX developers wanted a similar level of flexibility? Have the right piece in place, even just as a stub?