It’s been released just a few days ago:
Upgraded my ER-X without any issues. Nothing changed config- or behavior-wise. Was curious about the fix for PPPoE offload, didn’t even know such a thing exists, but:
noobient@ubnt# set system offload ipv4 pppoe enable Error: platform does not support IPv4 PPPoE offload Value validation failed Set failed  noobient@ubnt# set system offload ipv6 pppoe enable Error: platform does not support IPv6 PPPoE offload Value validation failed Set failed 
Alrighty then. Same goes for the new bootloader stuff, that doesn’t seem to apply to the ER-X (yet?):
noobient@ubnt:~$ show system boot-image The system currently has the following boot image installed: Uboot version: UNKNOWN
Even after multiple reboots. Oh well, nothing exciting to see here. Except for the warm, fuzzy feeling that you’re running on the latest and greatest again, of course.