Hi James
I've been working on a solution to the "stack" problem - photo at this link
https://www.dropbox.com/s/myyuq34h4ew1q ... .07.32.jpg
It works by using the new extra 9 gpio as a "stack" - plug in boards take one or more pins from the stack and the rest shuffle down in numerical gpio order. This way every board takes the gpio it needs from the bottom of the stack.
There is also a similar arrangement for the eeprom addressing that rotates a bit mask past the eeprom address pins. This means the first board plugged in has an eeprom address 0, the next has address 1, then address 3, and finally (or thereafter) address 7.
The original 26 pins are carried through as normal, so legacy boards can be attached. The gpio stack is useful for SPI chip enables.
It be good to discuss the merit and problems with this approach. We have our Melbourne Pi Jam tomorrow and I look forward to getting feedback from those guys too
regards
Lachlan