Assuming lens technology is fairly constant (lens sizes will not change much), and computing technology and chip/sensor manufacturing is always advancing, and that a larger sensor will always be able to collect more light, hence give a better picture, then I would venture to guess that full frame sensors will be used in the lower end dslr and even larger than current full frames will be used in the professional line. Since the camera chassis's size is unlikely to change and advances in materials will allow it to be thinner which will provide even more room, and the processing unit will be smaller or the same size, and the power source will either be smaller or the same size, and the components will produce less heat, then I would be shocked if camera R&D just decided to stick with partial frame sensors as it would lead to a stagnant market not to far in the future.
Either that, or lens technology will drastically change, which would result in starting over anyway.
technology from the slr market trickles down to the P&S, however, since the size of the lens is not as big of a factor, miniaturization will continue to take priority in the minds of many consumers. Within the next 5 years, I would venture to say that P&S cameras will approach the 20mpix mark, which will allow digital zoom to be less of a problem, thus further reducing the size of the camera. Its will become, even more than is so today, a completely different market.
That was my logic at least which led me to believe that with in the next 5 years there would probably be full frame senors in the prosumer category.
Any thoughts?