In my rev 1.d board revision I made a few modifications to make the development board more suitable for daughter boards. Here was my original rev 1.c board:

You can see that the power switch, although located on the side, wasn't optimal for shields since it was protruding upright instead of at 90 degrees to the board. The user programmable switch was also not optimally positioned, as it would also be unreachable if a shield was used. Instead, in rev 1.d I added a new power switch and user programmable switch that was flush with the edge of the board, and was angled at 90 degrees in order to be accessible if a shield was present. I also got rid of the smd buttons and opted for the through hole variety that could be mounted either on the front or the back of the board if need be to provide more flexibility in prototyping. Finally, in rev 1.d I added a VIN pin, so voltage can be input either from a shield, or through some other means. You can see the changes made in the current rev 1.d of the board:

And here is the rev 1.d board with straight pin headers to accept a shield: