Nim is great for embedded! I have that Waveshare frame and I plan to write Nim firmware/driver for it. It has no wireless connectivity though, only usb/microsd.
I have that device, it has no wireless connectivity (built on rp2040). The only IO is usb and microsd card (hijack for spi?). I have Nim drivers for a similar rp2040 based product (Inky Frame) which works great and has wifi/bluetooth (Pico W).
As of now FrameOS doesn't run on rp2040.
I have written drivers for Pimoroni's Inky Frames (based on Raspberry Pi Pico W) in Nim, but I don't own an Inky Impression. The code should be pretty similar once it hits the SPI bus.
I have planned to write GPIO/SPI/I2C "drivers" in Nim that interfaces with the Linux drivers. So far I have made a wrapper for libgpiod. https://github.com/daniel-j/nim-gpiod