OR any cube-based geometric design for that matter. 

This idea would greatly improve the extensibility of ideas and designs for more complicated modules that need say more than one stack.  (i.e. - a few home-brewed circuits on the sides of a main controller shield stack).

Hey

What about a shield with one or more:
- infrared LEDs
- sensors operating on the same frequency / range? 

The idea is that these little shield modules could talk to each other over distance (line of sight) using the equivalent of Morse code or whatever the programmer decides. 
( Also, you could have your shield change channels for you on your TV.    )