I saw below a question asking if a PiZero W was OK to use instead of the regular PiZero. Are there any restrictions to using the bigger boards like the Raspberry Pi 3? The hardware should all be compatible, and presumably there wouldn't be any restrictions in the software either, so I can't see why not. Even though the bigger boards will stick out from the nice compact shape designed to work with the Zero, it might give a bit more of a computational boost to not only manage the effects but also carry out other stuff in the background like signal analysis/working out keys/string tuning etc.
I'm planning to try this, once my gpio cable arrives. Now I'm using PedalPi with PiZero W. I don't have RPi3, I have just RPi1B+ and RPi2, but I'll let you know. I expect it to work out of the box.
From this image, you can see which resources are used in the pedal-pi:
So the GPIO18 and GPIO13 are needed to generate the PWM audio, having a look to the headers:
Seems that the Raspberry Pi B+ (1+) is compatible with the pedal-pi.
I have never tried it, so I cannot verify that it would work, but from the data seems that the www.raspberrypi.org/products/raspberry-pi-1-model-b-plus/ can work (although mechanically, you would need to use some jumper wires because the shield and the Rpi may crash into each other)
Ok, so I've tried RPi1B+ and RPi2 and neither of them works out of the box. On RPi1B+ I get some noise when trying sound generator, but buttons don't work. RPi2 is quiet. LED is also dead for both RPis. I've tried just take RPi Zero W card, put it into "big" RPi and run. I haven't debug it more. Maybe it's just some stupid software issue, but don't expect it to work as is.