zfs isnt as flexible as btrfs IMO eg Cant remove physical extents and rebalance. btrfs is the default fs in suse. and apt-get automatically snapshots every upgrade and you can rollback or co-exist even version upgrades although it requires command line to do so. I doubt ZFS even comes close on that score. Pretty awesome.
ZFS can now remove devices
at least 6 years ago opensolaris, you could do a upgrade, it would automatically snapshot the rpool and reconfigure grub for the new OS, but give the current one its own boot option for the kernel and a clone of the root filesystem pre upgrade that you could easy boot back into as if nothing have happen. (only gotcha was then manually upgrading the zpool verison on the disks that could not be understood by the old system).
So ZFS can do the automatic snapshot and stuff, just needs to be implemented by the distribution.