Agreed, I am no engineer either so it is pure conjecture on my part, and I meant no offence in the discussion. I guess I am assuming that in the same way we keep cramming more transistors onto CPUs, and make bigger and higher res Plasma/LCD/LED devices, then the same cost-challenges with sensors can be overcome. Of course making a 12 MP FF sensor for $500 this year, which may have cost you $700 2 years ago to make, also means you can make an APS sensor for $300. So the economies of scale would apply to either.
I guess my point was more that overall cost, simplifying your whole range has an affect on a whole manner of elements - from develop/manufacture/market to support and thus help reduce your cost base and allow you to increase your margin or lower your prices. Whether that was standardise on FF or APS would have the same affect to your cost base. I was just biased as would hate them to standardise on APS sensors
CMOS process is a relative stable process and has been around for a long time.. We cannot expect any substantial cost reduction in sensor from the process alone, except moving from 8 inch wafer to 12 in wafer. With the same amount of physical work (mostly done with automation), a little more chemical, and a slight modification in process and you end up twice as much sensor.
As for improving the sensor performance, we should have high hope. just look at the latest sensor from Nikon( Sony). However, we have already pushed beyond the capability of the lens resolution with 18MP APS_C sensor.
As a foot note: Most other electronic device are enjoying huge cost reduction in the last 40 years due to the advance in processing technology and cost reduction in the processing itself and hence the internal device on the silicon is getting smaller and smaller and resulted in the actual silicon in each IC is getting smaller and smaller and hence more and more IC per wafer. They are getting cheaper and cheaper. Unfortunately. This does not appy to the DSLR snesor. The sensor size is fixed. So there is no cost reduction in shrinking internal device. Instead we end up with higher pixel count. We have moved from 2MP (APS-C) to 18MP (APS-C) in the last 15 years or so.
As for the prine difference of FF and APS-C, The size ratio between them is about 2.63. So the cost ratio between FF and APS-C will be 5 to 7 times depends on the cleningness of the fabrication facility.