Hey Mikrotik, for a start, why not just buy OEM GPON SFP modules, certify they work with ROS, rebrand them and sell them, under Mikrotik brand?
Look into this topic: viewtopic.php?f=3&t=116364
You can get GPON SFP that will work with Mikrotik, but if you just need one, you pay extra $$$ and Chinese sellers just doesn't care about you, so no support.
But if Mikrotik made a big order, they could easily specify hardware so it's 100% compatible with routerboards, according to all the specifications they have.
Also add custom dialog for GPON provisioning to ROS, so you can set all required parameters easily from ROS.
All the required work is just in software, the hardware exists and works, but configuration is cumbersome and there are some issues with how ROS reads SFP EEPROM values etc.
There is clearly market for GPON modules, so let's make it happen.