> Using video interfaces to transfer arbitrary data at high speeds is becoming a common trick for cheap boards with limited interfaces.

There is a line in the book Accelerando about how evolution did this with biological vision.

It's basically the highest bandwidth sense we have and evolved AFTER smell (chemical based) and auditory (gas pressure based) senses.

unfortunately the ECP5-5G FPGA (with the SERDES/PCIe option), costs way more than the ECP5 (without SERDES). The Pi-5's MIPI interfaces gives you 8 parallel LVDS lanes that can run at 640 MHz each which is manageable for a cheap FPGA.