The writing was on the wall when it wasn’t shipped with Snow Leopard, in fact Snow Leopard had even worse zfs support than Leopard did, and that’s saying something.
The ZFS project has been discontinued. The mailing list and repository will also be removed shortly.
I’m guessing it’s something to do with NetApp patents and Oracle’s acquisition of Sun that put the final nails in the coffin.
I really hope that Apple are working on a next generation filesystem as HFS+ is pretty crufty these days. The stuff it does behind the scenes to make stuff “just work” is pretty ugly, and that’s only the bits that I actually know about. Things like the implementation of hard links? Bag-o-balls. How about permissions? I’ve never seen any other OS just lose permissions on files and need them to be repaired, how does this even happen? I suppose Apple needed something to put in to Mac OS X that would replace the “Rebuild the Desktop” AKA “Take two asprin and call me in the morning”
Maybe we’ll see something cool like btrfs one day?
Interestingly enough though, btrfs is a creation of Oracle… Btrfs also leverages a lot of the work that Sun did on zfs and learns some valuable lessons from the outcomes of the design decisions made in the initial stages of zfs.