Isn't there a problem with ZFS' memory footprint to be usable for desktop systems?
Apple sells far more iOS devices than Macs these days, and the iOS filesystem is case-sensitive HFS+. It's hard to imagine Apple doing something new in filesystems that doesn't improve the platform they make the most money from.
In a way, the same logic applies to Macs. The number of Macs that support multiple internal disks will soon be zero if it isn't already, so some of the best features of ZFS are irrelevant on new Apple computers.
I just finished reinstalling Yosemite an hour ago after wiping the HD of a friend's new laptop. It would not allow me to get past the eligibility check until I logged in with a valid Apple ID.
For the vast majority of people this will never be an issue as the machine comes pre-installed and re-installing the OS is generally not required unless something major goes wrong.