the only thing i can figure is that they were grooming zfs as a successor, but it was taking longer than expected. now i guess they have to go back to the drawing board and think of something else.
It's not like they built another OS - NeXT had one ready to go - even ported to x86. IIRC, all previous attempts to write a new OS to succeed MacOS classic failed miserably.
What advantage NeXT brought is that it's a very modular OS. Unix programs, traditionally, don't look the OS from too close and that makes swapping file-systems easy. Or, at the very least, possible.
Don't forget stuff like time machine is tied into some of Apple's FS hooks.
And of course the fact that the high end (apples market) is undergoing a pretty major shift in hard drive technology at the moment (SSD's).
Although performance is a nice feature, the most important things in ZFS are the zero-cost snapshots (very nice for backups, versioning etc) and redundancy and data corruption prevention. I love each and every file on my drive and I want their contents correct.
As a longtime XFS user, I can tell you that it has pathological problems when used anywhere near a user's desktop: unlinking is abysmally slow (and even worse under rm -R). It also has a habit of delaying flush for way too long, both using up piles of kernel memory and making itself extremely vulnerable to power loss.
If SGI has the copyright, they can still relicense it for use under OSX. I don't think Rackable would block this idea.
I've an Octane at home, which is my main machine except in the summer when it makes my flat too warm :-)
Apple should stick to fancy buttons and animation thanks.
My explanation is that filesystem performance on desktop and laptop systems is not that big a deal; while on larger servers like what ZFS is targeted for, filesystem performance in all facets is very important.