Fiber modules have been around for some years. The picture below show a 14.- USD 8 x Ethernet/2 x Fiber Mux/Switch that can be found on AliExpress etc. I have also seen smaller modules and 16 x Ethernet modules in the same price range – also boxed versions.
The interesting thing about these is that the Fibre links in theory can stretch a cable up to 100km. As I mentioned this has been around for decades, but it impresses me to see these modules down below 20.- USD in cost.
My own PLC uses high speed SPI as backbone and I already have Ethernet through Raspberry PI or ESP32 Board, but I fancied drawing a dual ethernet solution based on Wiznet W5500 as well. I have used this chip before. Ethernet and Fiber will extend the backbone to cover kilometers of wired net then needed. I am also a bit interested in using Ethernet as backbone all over, but space is a bit limited on the current Hat format. If I am to upgrade to Ethernet as backbone I will need to increase size, so having an Ethernet adapter is a compromize.
The ESP32 Ethernet module contains Ethernet and Wifi, but the SPI on it reduces backbone speed to ca 9Mhz as Slave. I can live with that, but I would prefer a higher speed. It is however challenges involved in using SPI the way I do, and a pure Ethernet backbone have a lot of advantages. But, is has one disadvantage – added space need on my boards + you need the switch in the backplane. And don’t forget that we also have CAN that can stretch over 1km.
Another option is to upgrade XPortHub and replace the SPI/I2C ports with an Ethernet port. I could just use magnets and a different, smalle connector etc. I have a bit of space problem here, but it can be done if I either sacrifice TF card or move TF card and/or battery to back side of card.