Some time ago, in Mikrotik RB922/RB921 QCA9557 & QCA9882 support? - #20 by xback, you mentioned:
I got someone on chat who is also interested and may provide the code for making the SFP slot work
Do you remember, by chance, who was that person? I got the slot to detect and talk to SFP modules, but I couldn't bring it up as a "regular" interface.
Cheers