From what I have heard, it's not that the 1020 CAN'T have the improvements, it's that they would have to code them much differently for the older processors. Given that Windows 10 is right around the corner, it seems they have decided not to expend the effort. Obviously the results would not be as good as a Snapdragon 800 regardless, but they could certainly improve it a lot. It's very unfortunate.
I have purchased a used 1520 of eBay so that I will be able to play with the new camera improvements. My biggest problem with the whole situation is that Microsoft seems completely content with no flagship until W10 comes out in nine months or whatever. The icon and 1520 ate now discontinued, so they aren't even currently selling a phone that will be able to take advantage of the new camera benefits in full. The 830 is nice, but completely hobbled by the processor and the camera is only 10 megapixel. Completely ridiculous.