Hopefully this hasn't already been asked, but what is the maximum number of GPIO pins that can be utilized on a current Raspberry Pi board? I know that there are 8 of them by default, and I've also read that it is possible to repurpose some of the special function pins to become GPIO. Unfortunately for the time being, there doesn't appear to be any more information about this process, or any limitations that might need to be considered when pursuing it.
I'm asking because of a potential project that would involve attaching this LED video panel to a Raspberry PI, but the panel requires 12 data pins. Ideally I would like to control the panel directly from the RPi, without extra circuitry.