Sounds like the "keyboard" would then have to have special hardware (pricey/not efficient) or the pad would have to have multicore/scalable hardware that draws more power when connected to the "keyboard" and the keyboard could have extra hardware like more storage and IO ports and a PSU/high capacity battery. It would be cool to merge this concept with something like padphone - sort of a Russian doll concept :) And the ARM manufacturers seem to be going that route for performance anyway - adding cores/disabling them for power saving. I assume the same concept could be applied to memory and GPU.