Here are some tiny suggestions, sorry if they are impractical, I am a beginner in electronics and mechanics.
often the 22mm screws are a tad too long and the 14mm are just too short. How about a set of 18mm screws ? I would order a 50-pack immediately.
Allow for a usb cable to provide power to the meduino and the base shield. Using things like a smart power base http://cobbaut.blogspot.be/2013/08/independent-raspberry-pi.html is easier (and lighter) than the battery pack.
Or you could make your own usb-chargable battery, because this smart power base from MTS is expensive (70 dollars is ok, but my country charges an extra 50 dollars import tax on this).
A gyro sensor would be nice, or is there a way to use the Lego gyro sensors ?
Maybe this works already ? I have one Hitechnic touch sensor multiplexer. It would be nice to be able to add four touch sensors on one port. For example on a round robot (think roomba-like) that drives around and bumps into things, it would allow detecting the bumps on all four sides, while still having room to add several other sensors.