This SFP stick is supposed to only convert GPON to Ethernet so you can log in DHCP/PPPoE using other routers, it's not supposed to do the routing, I agree that it shouldn't run OpenWRT on this particular model, there's a similar GPON SFP having a dedicated RAM chip and it's run Linux like the Zisa Support Zisa OP151S GPON ONU Lantiq SFP module