The GPIO seems to be pretty lacking on the one I was playing with. Also, it's an older ARM core (unless there was a newer one they released I didn't know about) so it is a bit slower in operation. My IO requirements at the moment are a TFT LCD display, SD card (which is obviously not a problem for the pi or the beaglebone out of the box), 2 ADC in at audio rate, 4 ADC in at LFO rate, 8 gate/trig in, 2 DAC out at audio rate, 4 at LFO rate, 8 gate/trig out.
That's an exceptional amount of IO. Not all used at once mind you. I just think getting all that out of the pi would be difficult, but maybe there is just something I misunderstand.