Validated with ZFS from focal-proposed, according to test case from description:
ubuntu@z-rotomvm34:~$ dpkg -l | grep zfsutils
ii  zfsutils-linux                       0.8.3-1ubuntu12.12                    amd64        command-line tools to manage OpenZFS filesystems
ubuntu@z-rotomvm34:~$ zfs list
NAME                 USED  AVAIL     REFER  MOUNTPOINT
rpool               2.50G  25.6G      176K  /
rpool/ROOT          2.50G  25.6G      176K  none
rpool/ROOT/zfsroot  2.50G  25.6G     2.50G  /
ubuntu@z-rotomvm34:~$ sudo journalctl -b | grep -i ordering
ubuntu@z-rotomvm34:~$ lsblk -e 7
NAME        MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
vda         252:0    0   30G  0 disk
├─vda1      252:1    0  512M  0 part  /boot/efi
└─vda2      252:2    0 29.5G  0 part
nvme0n1     259:0    0  9.8G  0 disk
└─nvme0n1p1 259:1    0  9.8G  0 part
  └─swap    253:0    0  9.8G  0 crypt [SWAP]

In addition to the test above, I've also tested the configurations suggested in the [Test Plan] section. Besides validating the ordering bug, I've also done basic smoke tests and verified that the ZFS pools are working as expected.

- Encrypted rootfs on LVM + separate ZFS partitions:
ubuntu@ubuntu-focal:~$ zfs list
NAME           USED  AVAIL     REFER  MOUNTPOINT
zfspool        492K  4.36G       96K  /mnt/zfspool
zfspool/tank    96K  4.36G       96K  /mnt/zfspool/tank
ubuntu@ubuntu-focal:~$ dpkg -l | grep zfsutils
ii  zfsutils-linux                       0.8.3-1ubuntu12.12                    amd64        command-line tools to manage OpenZFS filesystems
ubuntu@ubuntu-focal:~$ zfs list
NAME           USED  AVAIL     REFER  MOUNTPOINT
zfspool        492K  4.36G       96K  /mnt/zfspool
zfspool/tank    96K  4.36G       96K  /mnt/zfspool/tank
ubuntu@ubuntu-focal:~$ sudo journalctl -b | grep -i ordering
ubuntu@ubuntu-focal:~$ lsblk -e7
NAME                         MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
sr0                           11:0    1 1024M  0 rom
vda                          252:0    0   30G  0 disk
├─vda1                       252:1    0  512M  0 part  /boot/efi
├─vda2                       252:2    0    1K  0 part
├─vda5                       252:5    0  731M  0 part  /boot
└─vda6                       252:6    0 28.8G  0 part
  └─vda6_crypt               253:0    0 28.8G  0 crypt
    ├─vgubuntu--focal-root   253:1    0 27.8G  0 lvm   /
    └─vgubuntu--focal-swap_1 253:2    0  980M  0 lvm   [SWAP]
vdb                          252:16   0    5G  0 disk
├─vdb1                       252:17   0    5G  0 part
└─vdb9                       252:25   0    8M  0 part

- ZFS on LUKS
ubuntu@z-rotomvm33:~$ dpkg -l | grep zfsutils
ii  zfsutils-linux                       0.8.3-1ubuntu12.12                    amd64        command-line tools to manage OpenZFS filesystems
ubuntu@z-rotomvm33:~$ zfs list
NAME           USED  AVAIL     REFER  MOUNTPOINT
zfspool        612K  9.20G       96K  /mnt/zfspool
zfspool/tank    96K  9.20G       96K  /mnt/zfspool/tank
ubuntu@z-rotomvm33:~$ sudo journalctl -b | grep -i ordering
ubuntu@z-rotomvm33:~$ lsblk -e7
NAME        MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
vda         252:0    0   30G  0 disk
├─vda1      252:1    0  512M  0 part  /boot/efi
└─vda2      252:2    0 29.5G  0 part  /
nvme0n1     259:0    0  9.8G  0 disk
└─nvme0n1p1 259:1    0  9.8G  0 part
  └─zfspool 253:0    0  9.8G  0 crypt
ubuntu@z-rotomvm33:~$ cat /etc/crypttab
# <target name> <source device>         <key file>      <options>
zfspool /dev/nvme0n1p1 /etc/keyfile luks

- ZFS on dm-raid
ubuntu@z-rotomvm33:~$ dpkg -l | grep zfsutils
ii  zfsutils-linux                       0.8.3-1ubuntu12.12                    amd64        command-line tools to manage OpenZFS filesystems
ubuntu@z-rotomvm33:~$ zfs list
NAME           USED  AVAIL     REFER  MOUNTPOINT
zfspool        612K  9.20G       96K  /mnt/zfspool
zfspool/tank    96K  9.20G       96K  /mnt/zfspool/tank
ubuntu@z-rotomvm33:~$ sudo journalctl -b | grep -i ordering
ubuntu@z-rotomvm33:~$ lsblk -e7
NAME        MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
vda         252:0    0   30G  0 disk
├─vda1      252:1    0  512M  0 part  /boot/efi
└─vda2      252:2    0 29.5G  0 part  /
nvme0n1     259:0    0  9.8G  0 disk
└─md127       9:127  0  9.8G  0 raid0
  ├─md127p1 259:1    0  9.8G  0 part
  └─md127p9 259:2    0    8M  0 part