I've been working on a project that merges Mesa firmware with generic FPGA boards sourced from Aliexpress. The link I'm going to give shows a half completed prototype, I'm currently waiting on the PCB to replace the proto board on the left. The major mod to the FPGA board is to replace the flash EEPROM with a larger capacity model. So far the interface is to a RPi via SPI.
forum.linuxcnc.org/show-your-stuff/50461-diy-7i90-ish
I also have a SODIMM fpga module that can be had for about $20 AUD + postage form Aliexpress that I have just finished working out edge connector to FPGA pin locations.
I'm hoping to be use this with 7i90 firmware via SPI and with 7i90 ssremote firmware.
Ethernet would require a bit of time to work on as I'm trying to stay within the bounds of the hostmot2 infrastructure.
That being said Mesa product are the most cost effective solution. This is just a project to keep my mind going until I can find employment.