Original GC not have USB port but a hi speed port and 2 serial ports, why not explore this way and create a firmare/mod for on GC acess a wii SD card(redirect a false hi speed port/serial port)??
btw i feel this a good time to remind you guys that sea of thieves was made by rare, who also made DKC1-3 and DK64, alongside banjo kazooie and conker's bad fur day