Interstate 75 looks great.
One suggestions is to bring more GPIOs to external header, especially the GPIO24 & GPIO25.
This would bring full SPI and full UART externally.
This could allow the use of interstate 75 as an fast interface card driven by another CPU board.
I echo this request!
I’d love to use the I75 to emulate an HD44780 LCD, but doing so requires 10 or 11 GPIOs, but this board only exposes 8 at most.
Please stop putting extra things on a board that then restrict its capabilities. Several GPIO pins aren’t even connected, and another three are wasted on an RGB LED. Another is dedicated to the “user switch”.