I drafted a GSM/Ethernet module as well as a 3xGalvanic RS485 earlier, but I am toying with the idea of attempting a PLC Module with STM32F405 using ESP32 for Ethernet/Wifi and 4-6 RS-X ports. 4 if used as PLC-module, 6 if used stand-alone. I have also 2 CAN ports if I can find space/pins for them and I actually have CAN/UART’s on ESP32 as well.
I could connect ESP32 to the backbone as illustrated below, but I have little data on it’s UART speed yet. It’s just an idea for now.
I have not made a move on my PLC concept yet for the simple reason that I have far to many designs/PCB’s that I need to work on and too little time as is. But, still fun to toy with ideas. ESP32 basically cost the same as a W5500 and can do both Ethernet, Bluetooth and Wifi. It will however need an external Phy for Ethernet.