I'd actually love it if this idea extended far enough to let me double my "phone" as an impromptu laptop/desktop. I know that we can use a bluetooth keyboard or whatever and kind of simulate things. But I'd love to carry around a single computing device that I can drop into a cradle at home and it's using my two big desktop monitors and nice keyboard/mouse, and when out and about, head into a coffee shop and swap the screen out for a larger screen and keyboard, and then head onto the subway and just swap the screen back and use it like a phone. Then end of the day, head to the gym and swap out a few parts and have it just play music for me while I work out. Head out for a hike on the weekend and configure it like the Gym, but put in a better GPS unit and a bigger battery or something. Go to the store and swap out the GPS unit for a barcode scanner so I can comparison shop a bit. If something breaks, I can fix it myself. Go home and plug it into an HDMI port and watch movies or play games or something. Want to read a book? Swap out the screen for an e-ink screen. Going on a trip? swap in the GPS device, big battery and the Nokia camera module so I can use my nice lenses and find my way to the sites. Swap the screen for the bigger screen later so I can review and edit my photos for the day.
I could trade my notebook, camera, desktop, console, media devices, mp3 player, e-book reader and tablet in entirely.
But all my data is present for me and I can work on it, context appropriate to the interfaces I have available at that moment.
I wouldn't mind having a few bits and parts floating around my backpack if it gave me the flexibility to do that kind of thing.