FPGAs are expensive as far as I can tell. If you can find me a FPGA with a similar amount of RAM as an ESP32 and comparable price point, I’m interested.
I’m actually making progress on the coprocessor! As of this afternoon, I have a sketch receiving SPI with the APA102 protocol at 4MHz using DMA (I2S In peripheral), writing to a 48bpp SmartMatrix buffer (taking advantage of the GBC bits in the APA102 protocol), refreshing a 64x64 panel at >120Hz 36-bit color. This is running on an ESP32 Pico board, with just a 5V->3.3V level shifter for external circuitry. There’s enough RAM to refresh a 128x64 panel if I add a SmartLED Shield circuit with address latch externally.
128x128 is a stretch goal I’m saving for later. It might be possible, but not easy.