But I thought that ZFS won't boot on any system. And that Apple was done with its fling with ZFS. Did I miss the memo?
Solaris (and its open-source derivatives) would always boot from it. FreeBSD and Linux now boot from it, after a bit of configuration voodoo.
The memo you missed is that after some fracturing among the various open versions, they got together and formed the OpenZFS group, which does some sharing of plans and code as updates are made. Since that time, the open-source versions have matured from promising curiosities into really great implementations. The older open-source version for OS X has died, and been replaced by a derivative of the Linux version, which is a strong piece of work.