where is the pi-400 M-2…since they migrated it into this key board just fit an m-2 controller and a back opening door to change out an m-2 drive…??
i would atm just add a usb3 to m-2 sata bridge …search the web for them…
note depending on your bridge tye you may need to add it to the cmdline.txt file if your booting off it or if it wont run on the usb 3 ports…but will run on the usb 2 ports…
my notes here…for making it work if the bridge is not migrated into the kernel…
on another note you could buy an argon base ssd housing and fit a usb dvd rom as a cover to it and run it with a usb hub this may also be a builders/makers dream …
another idea for core they could make top covers for them another core made product… and there would be no extra code added as they are 100% compatible with the rpi-4 boards…just the ned for a good quality usb3 lead …i have one right here it is approx 20 cm long male to male blue connectors and approx 8 mm thick cable…i don’t know where i brought it from …sozz…
