Personally, I can see them going a slightly different path. Two things caught my attention in apfs - 'space sharing', where two volumes can take the same exten

Personally, I can see them going a slightly different path. Two things caught my attention in apfs - 'space sharing', where two volumes can take the same extents on disk, rather than having non-overlapping bounds (in practice, if not implementation, this so far acts as if its one volume, where members are tagged with which filesystem they belong to) - and linked clones for copies. It doesn't seem inconceivable to me that the 'recovery volume' holds a copy of the OS, and the installed OS is just linked clones to the recovery volume. On the surface this is a lot like how we treat unixy hardlinks, but a) linked clones can diverge from each other on a block-by-block basis, rather than "you're a link or you're not". and b) because two filesystems can take the same physical location on disk, a linked clone _could_ (and this doesn't appear to be possible in the current developer previews) act as a hardlink across volumes. I realise this seems like a lot of effort with little gain, but the 'how' seems to be all in place - and with SSDs setting us back a step to 256GB volumes at the entry tiers, the space-savings wouldn't be unwelcome. .. or this could all be hand-wavy nonsense. But there does seem to be some interesting features in apfs, and I really an curious to see where they go with them - apple rarely do nuts'n'bolts changes this big unless they have a use-case waiting for them (like spotlight & the fs_usage API).