Wow nice to see the pictures and mechanical detail. I always find that a challenge to get integrated early – mostly because I’m doing everthing. Is it part of an open source project? sounds like its for a specific translator/extender fiber optics to copper RS485/RS23 In looking over the Rpi PICO, while an amazing processor with program stored in a serial flash device, seemed like there wasn’t a lot of serial peripherals only 2 UARTs . At least for me that was show stopper.
I’ve just posted on a project I’ve been chipping away at https://www.envirodiy.org/topic/using-samd51-wio-terminal/ and it has the USB drivers for the drag and drop bootloader programming with the .uf2 file :), which hopefully can also be good for remote OTP (over the air programming)