Está lá no meu sistema:
$ locate zfs
/boot/grub/x86_64-efi/zfs.mod
/boot/grub/x86_64-efi/zfscrypt.mod
/boot/grub/x86_64-efi/zfsinfo.mod
/lib/modules/4.4.0-10-generic/kernel/zfs
/lib/modules/4.4.0-10-generic/kernel/zfs/avl
/lib/modules/4.4.0-10-generic/kernel/zfs/nvpair
/lib/modules/4.4.0-10-generic/kernel/zfs/spl
/lib/modules/4.4.0-10-generic/kernel/zfs/splat
/lib/modules/4.4.0-10-generic/kernel/zfs/unicode
/lib/modules/4.4.0-10-generic/kernel/zfs/zcommon
/lib/modules/4.4.0-10-generic/kernel/zfs/zfs
/lib/modules/4.4.0-10-generic/kernel/zfs/zpios
/lib/modules/4.4.0-10-generic/kernel/zfs/avl/zavl.ko
/lib/modules/4.4.0-10-generic/kernel/zfs/nvpair/znvpair.ko
/lib/modules/4.4.0-10-generic/kernel/zfs/spl/spl.ko
/lib/modules/4.4.0-10-generic/kernel/zfs/splat/splat.ko
/lib/modules/4.4.0-10-generic/kernel/zfs/unicode/zunicode.ko
/lib/modules/4.4.0-10-generic/kernel/zfs/zcommon/zcommon.ko
/lib/modules/4.4.0-10-generic/kernel/zfs/zfs/zfs.ko
/lib/modules/4.4.0-10-generic/kernel/zfs/zpios/zpios.ko
/lib/modules/4.4.0-13-generic/kernel/zfs
/lib/modules/4.4.0-13-generic/kernel/zfs/avl
/lib/modules/4.4.0-13-generic/kernel/zfs/nvpair
/lib/modules/4.4.0-13-generic/kernel/zfs/spl
/lib/modules/4.4.0-13-generic/kernel/zfs/splat
/lib/modules/4.4.0-13-generic/kernel/zfs/unicode
/lib/modules/4.4.0-13-generic/kernel/zfs/zcommon
/lib/modules/4.4.0-13-generic/kernel/zfs/zfs
/lib/modules/4.4.0-13-generic/kernel/zfs/zpios
/lib/modules/4.4.0-13-generic/kernel/zfs/avl/zavl.ko
/lib/modules/4.4.0-13-generic/kernel/zfs/nvpair/znvpair.ko
/lib/modules/4.4.0-13-generic/kernel/zfs/spl/spl.ko
/lib/modules/4.4.0-13-generic/kernel/zfs/splat/splat.ko
/lib/modules/4.4.0-13-generic/kernel/zfs/unicode/zunicode.ko
/lib/modules/4.4.0-13-generic/kernel/zfs/zcommon/zcommon.ko
/lib/modules/4.4.0-13-generic/kernel/zfs/zfs/zfs.ko
/lib/modules/4.4.0-13-generic/kernel/zfs/zpios/zpios.ko
/usr/lib/grub/x86_64-efi/zfs.mod
...
É um sistema de arquivos para containers ( LXC, LinuX Containers ) então não para o sistema operacional em si. "ext4" será o sistema de arquivos do Ubuntu pelo menos nos próximos anos.
Eu não posso escolher em gParted (pelo menos ainda não):
