I was also able to cobble together this example of a little 2D coordinate system. This could be done using sound propogation if processors had microphones, or with a projector that sweeps the smart-painted wall with a few lines of infrared light. The infrared light beam is rapidly modulated with coordinate information. For instance, processors could be hard-wired or downloadable , where downloading would be done by some sort of mass broadcast. This might be done by sound, light, or radio waves.
Infrared sensors are reliable and cheap, so are good candidates.
Whatever system is used to broadcast instructions might also be usable as a power source. I'd really like to see these things realized, and I'd really like the chance to try programming real ones. Maybe someday I'll figure out how to build them. Here are some links to related things, which I haven't yet sorted by interest or utility.