A Beowulf type cluster would be extremely inefficient unless you just wanted to use it as room heater.
alternatively, if you needed a microcontroller platform, there are much faster Platforms.Such as?
For input pins, you need to use logic shifters for the due, to prevent it from being damaged. Do they come on a shield or are they discrete components? Input & output pins?
Has anybody built a Beowulf cluster of Due boards because ethernet shields are available?