you are requesting to add gpon functionality to hap lite for free!!
i think that kind of improvement can rise the cost to 50us at least and im being optimistic, and i thing hap lite cpu only can attend gpon bandwidth on full fast-track mode, keep in mind it only has 10/100 ethernet ports!!
for gpon speeds and using functionalities of routeros i think the rb3011 its more adequate
rb3011 already has the sfp socket, theoretically with the sfp module you can connect to gpon, and it has gigabit ports and at least 4.0x the performance of hap lite cpu
in the wireless area i think gpon needs to be paired with 802.11ac 2x2:2 to take advantage of the speed