Hi Marcin, welcome to the lafibre forum. Your PLNOG18 videos on ONT design have been inspiring to me. I was hoping that one day you would land here or on openwrt and help us with ONT interoperability.
Since you know so much about Realtek, do you know why SFP with the RTL9601C SoC responds as RTL8672?
# cat /proc/cpuinfo
system type : RTL8672
This is the chip for SFP V-SOL V2801F sold in Europe under the names CarlitoxxPro CPGOS03-0490 v2.0 or OPTON GP801R.
RTL8672 is a platform, I mean - there is a separate chipset with this name for routers. And RTL9601C/D is 8672 plarform with additional function blocks necessary for GPON operations.
This is how SoC's are build. There are function blocks that vendor can add/remove depending functionality they need.
Same way, it is quite simple to replace MIPS core with ARM core, as this is just a CPU block. Of course on silicon level it is bit more complicate to prepare proper litoghraphy for manucacturing
Similar way intel makes CPUs, and sometimes it is cheaper to build a common silicon desing and later on to disable/enable function blocks/cores by fuses.
Btw, OPTON is a brand of cdr.pl, my former neighbor from same housing block. They just resell equipment making lot of money, but without support.