Shield for Arduino Due is available. The information for Arduino Mega 2560 above is the same with the exception that the shield work only with Arduino Due. Arduino due is 3.3V based MCU. The Arduino Due shield will only work with 3.3V MCU.
Arduino Due is faster platform compared to Arduino Mega. It also has more GPIO interrupt support. I am have specific version of GPIOProxy for DUE as an example.
I am personally are building multi relay system. I am up to 24 relay now. I planning to see if I can build something up to 64 relay. The challenge is supplying power to power the relay. It will require a lot of current if one need to turn on all the relay. The type of relay you see below is a mono-stable relay. The relay has 2 positions. It will require power on one position.
