There is more going on than just this, but I thought I'd just post this tidbit for now.

I had a discussion with Delicon yesterday and discovered that the ARM is more flexible in how it handles IO than previously thought. I was under the impression that its pins were already accounted for. As it turns out, the IO lines that are currently assigned to the two UARTs, I2C, and SPI can be reassigned at runtime, and that there are enough unused GPIO pins that they can be swapped in their place. What this means is that we should be able to hook two extra controllers through the cartridge! Besides the prospect of having extra controllers, we may also be able to do the "hardware assisted" paddle reading that was discussed a while back in the forums. With hardware-assisted paddle reads, all new types of games suddenly become possible that otherwise weren't because of the CPU drain of traditional paddle reading. The paddle pot reading may not happen if the ARM doesn't have enough free time to keep sampling them, but the joystick lines definitely sound doable.