The limiting factor is the bootloader. Mac firmware can read HFS+ natively, find the bootloader, which in turn recognizes HFSX, Apple RAID, and Apple Core Stora

The limiting factor is the bootloader. Mac firmware can read HFS+ natively, find the bootloader, which in turn recognizes HFSX, Apple RAID, and Apple Core Storage. I doubt any of the previous ZFS support exists in the current bootloader. Unlike linux where there's a separate /boot, OS X doesn't really separate boot from root file systems. So how you'd boot XNU from HFS+ and transition to a separate ZFS root fs isn't obvious to me from the existing documentation.