I upgraded today and also received the message regarding nss-myhostname and systemd. In addition, I received the following messages during the upgrade:
$this->bbcode_second_pass_code('', '
2013-01-21 17:20] ==> Warning: setcap failed, falling back to setuid root on /usr/bin/systemd-detect-virt
[2013-01-21 17:20] ==> Persistent net naming rules have been shipped as disabled.
[2013-01-21 17:20] See /etc/udev/rules.d/80-net-name-slot.rules for more detail
')
Post upgrade, I rebooted my PogoPlug and it came right back up.
Unfortunately OXNAS is well behind the rest of the Arch user base. Arch has retired init and transitioned to systemd while the older OXNAS kernel doesn't support systemd. This has and will continue to cause issues as individual packages drop their support for init.