Did you ever find a solution? Seems like something I also want to accomplish?
The raspberry pi idea looks good but i also would like to change the GoPro settings and see the video feed all while in flight.
Current Tx does not support enough channels to even attempted anything more then triggering the shutter.
I really would like to avoid opening the hardware of the GoPro but feel confident (if provided some direction) in wifi/python or if possible connecting the serial ports of the GoPro and Raspberry Pi.
I'm also concerned about the 2.4GHz transmitter and what i believe 2.4GHz wifi the GoPro is using.