The PSoC4 Pioneer Kit comes with full documentation, gerbers etc. Will that help you?
Seems to be some psuedo specs here - playground.arduino.cc/Learning/ArduinoSpecs
I have never seen any association specs as of yet, IEE, etc, but I make no claim to
being an Arduino expert. Of course the Atmel chip spec probably makes most sense
because of the direct interface environment, for the most part.
I think you would get better asnwers asking on the arduino forums.
First you have to make it clear if you want to make an arduino shield that will be compatible with arduino or are you going to design a board that will have the arduino form factor and so be able to connect to arduino shields.
Building a shield or a motherboard, Atmel chip specs foundation,
most pertainent. But you are still faced with power up/down specs,
if a deprature from the chip specs, hot plug or no.......