Do you remember that we saw Apple file those patents for some new displays a while ago? One of them was to be able to control the OS with various 'gestures' made by the user, e.g. pinch two fingers together to drag a file or app around the desktop. But there was another one which said something about having a camera of some sort behind the display. I think that that would be the way to go for the Mac mini and the upcoming Power Macs.
However what if you want one of these displays with your MacBookPro or Intel iBook (whatever it may be called). Assuming they put an iSight in the new Intel iBook, you would have two iSight cameras on one machine. I don't know if anyone has ever tried connecting an iSight into a new iMac or MacBookPro, it probably wont cause much of a problem, but you could possibly set up multiple angles. I agree that they would in-fact have to lower the price or make small displays as no low end consumer will pay close to $1000 for a display.