Which scenario is more likely in the future?
1. If we ever reach anything resembling that limit we will never need to buy another camera again.
2. If cropped sensors are good, full frame is better for the same pixel count. You can simply catch more photons with a bigger receptor. If both are so good that you can't tell their quality apart, full frame still have great benefits for diffraction limits and thus will still be more desirable for the shallow depth of field crowd.
3. The sensors are still the most expensive part of any camera. P&S aren't priced for larger sensors and I doubt ever will be. A bigger sensor means bigger glass, and ultimately that means it no longer fits in your pocket.
So I say 1 despite being certainly unlikely to happen it is still more likely than the other 2.
Look at film cameras - (some) full frame P&S (film) cameras are comparable to the size of crop P&S digital cameras of today. APS film cameras are probably closer to the size of digital cameras today though.
I have to disagree with this. Even the smallest 35mm cameras ever made compare in size only to bridging cameras with typically slightly larger than normal sensors. Sure width and height they were tiny, but still 3 times thicker than the cheap $150 thing my sister has which itself doesn't win any size awards.
APS cameras maybe, but consumers in general aren't going after fixed focal length digital cameras. They seem to want it so thin it'll slide through cracks in the pavement, so small it can fit in a pocket, so versatile it has a 500x zoom on it, and with the highest possible quality. All of those are at odds with each other and the zoom factor for versatility often wins out. There have been a few larger sensor P&S cameras compensated by a fixed focal length lens to keep the size and weight down, and they have all been quite sub-standard in sales.