Certainly is and will be for the next couple years but they probably missed the boat on this one, especially now when new technology is just around the corner.
New NG-PON deployments should drive xPON prices down on the second hand market not to mention plenty of choices from Korean and Chinese vendors.
MK last adventure into xPON territory did not go too well. As you heard, GPON SFP ONU was discontinued.
We’ve been asking for over 2 years to make Mikrotik SFP ONU configurable.
http://forum.mikrotik.com/t/usage-gpon-module-sfp-in-spain/104807/1
At the end we voted with our wallets and purchased SFP ONUs from other vendors, willing to accommodate our requests.
And, +1 for Mikrotik full size ONT as long is not restricted in any way.