Dslr sales are falling because the main manufactors aren't giving a good reason for people to upgrade. They are repacking the same tripe for the past few years. If they want dslr sales to improve, they need to sell their "regular" dslr with the same quality as their cinema line. They need to innovate -- add more features, etc. Perhaps make their camera's even smaller, etc...
In the audio/visual field, there are many manufactors who aren't losing sales. For instance, you have gopro, you have blackmagic, etc. Granted I agree with a lot of people -- we are at the point where the camera doesn't really matter for the film makers. Movies and features can be made with almost any camera now. HOWEVER, people do buy products that are "compelling". Look at gopro. How many people are actually going to go wingsuit flying.. OR motorcrossing? OR swimming with sharks, etc... However, these same people buy gopros by the boatload -- gopro's are "compelling".. they are the best at what they do at a price point where consumers will buy.
The dslr manufactors better start introducing "compelling" products @ a price point where consumers will buy or else they will be left behind... actually, they are already starting to be left behind.