Here is the way I see it, my vision is probably not so good, but I will tell you what I think.
When film was king you could get away with keeping a camera body for a long time because your camera would get better as the film got better, Film makers made money and drew in new customers by making the film better and better. Camera makers kept money coming in by adding and dropping a few new cameras into and out of their line up every year or so.The only reason people bought cameras is because they wore out (Pros), there was a new gota have feature (Auto focus), they wanted something better (this point and shoot sucks), the old one was stolen, they broke the old one.
Now the film is integrated into the camera in the form of the sensor so if you want a better resolution photo you need a newer camera. Never mind that a 6MP camera can shoot a photo that can be printed 12 x 18 easily, no we need more resolution. I hate to say this, but until the sensor in a DSLR matches what 35mm film can do prices will keep doing what they are doing now. I think it is funny that people want better resolution, but the average casual photographer is going to get 4 X 6 prints, or only look at them on their computer screen that is not all that high res anyway. Pros are going to do big prints, and wear out equipment, but there is a limit to how large most pros will print, who really wants a 22 X 34 poster of themselves, really? Pros will probably take the hardest hit because prices will increase on a sharper curve as performance and price go up sharply every year, but you use up a camera in about a year or two, maybe three on the outside it's going to hurt. Eventually performance and price will hit a plateau and old digital will stabilize and prices for used equipment will be more like they were for film equipment before digital came along.
One thing really puzzles me in all this, I hear pros all the time say "I sold all my Nikon gear and went Cannon, then I sold all my Cannon gear and had to buy all new Nikon gear" Or the other way around. What is with this "ALL" my gear thing? I want to know why when you swap systems don't you keep your glass? Maybe not all of it, but at least keep the best, and hardest to replace stuff. You know you are lying when you say you will never go back, and even if you don't go back glass holds value better than a body, sell it in a better market, or at least wait until you are sure your staying. I was a mechanic for a lot of years so maybe that is my problem, mechanics never use the word sell when talking about their own tools, then again tools have played nice across systems starting with Snap-On in 1920, cameras not so much. Also I have ingrained in me the "as soon as I get rid of it I will need it" mentality.