Hum, I think the problem with this is going to be using i2c on the Ubiquiti to upload the firmware. I can't see any way of doing that at all. The show interfaces ethernet eth5 sfp command basically runs the command
/usr/sbin/ubnt-hal getSfp eth5
which is presumably some sort of Ubiquiti hardware abstration layer for the MIPS based chipset being used. When I try and use ethtool to read the EEPROM I get the following
ubunt@gw:~$ /sbin/ethtool -m eth5 Cannot get module EEPROM information: Operation not supported
I also get the same error on a an Edgerouter Infinity at work. So it looks like the EdgeRouters have some sort of propriatory interface to be able to talk to SFP's over the i2c bus, and without any help from Ubiquiti then supporting the Metanoia G.fast SFP is a none starter I think.
On the plus side the Metanoia VDSL SFP does not require a firmware upload, and I understand a fair bit about the fabled EBM now. Enough I think to tempt me into buying one.