I think that today is possible to include ZFS in Leopard... i explain why
Porting of ZFS for FreeBSD is near complete:
Pawel Jakub Dawidek is manteiner of this porting, in a recent post he write:
"I've almost all file system functions working.
I started to run some heavy file system regression tests. They work."
this from
http://www.opensolaris.org/jive/thread.jspa?threadID=12766&tstart=0
We also knew that zfs can now boot from x86 ZFS machine
http://opensolaris.org/os/project/zfsboot/
Using EFI booting for boot from ZFS i thinks i more simple...
ZFS respect POSIX standard that explain that appz don't need to edit to func with ZFS.
What does you think?