1) AFAICT they didn't relicense any of the ZFS code, just dtrace.
2) Even if they had, GPLv2 code still wouldn't be able to go into xnu.
3) Even if it could, Apple has long since moved on from ZFS. They've taken the time to write a new filesystem (APFS) already, so it's hard to see them having any interest in ZFS at this point (and yes, I know APFS doesn't have all the features of ZFS).
