The success of the D500 is proof that the nay-sayers, including Nikon's marketing department, reported the death of pro- and prosumer level DX prematurely.
Nikon marketing always try to sell what products they currently have. Anything else would be working against the company's best interest and their shareholders and potentially lead to the Osborne effect.
Some interviews with higher level Nikon execs were much more moderate, and they said they knew many of their customers preferred the narrower angle of view of DX cameras and Nikon hadn't forgotten their DX users. This was a few years ago e.g. in the Nikon Owner magazine published in the UK. Looking at the D500 today it seems obvious they wanted to get it
just right and before the Multi-CAM 20k it wouldn't have had the same impact. It would have been just an expensive, fast D7200. With Multi-CAM 20k it became a product which is clearly ahead of its competitors in telephoto action photography, and yet not take anything away from the D7200 in the much lower price class.
As for the long flange distance, it is what it is, but that very same thing allows such excellent coverage of the sensor area with AF points. DX DSLR with a shorter flange distance would not have space for the Multi-CAM 20k. A mirrorless camera with integrated phase detect points is more limited in handling situations where the focus is far off; the range of phase differences that can be measured by a DSLR focus sensor is greater, which leads to almost instant focus acquisition with fast teles. For wide angle mirrorless has its own advantages, and I would not be surprised if mirrorless cameras had better AF when using a fast wide angle prime. I don't think these relative merits are going to disappear over time. Time will tell how the products evolve but it is nice to see such diversity of camera types today compared to the past where there were fewer options.
For me a mirrorless camera isn't going to have an EVF; I will choose models which have LCD and an optical viewfinder I was just trying out the Fuji X-T2 and when I pressed the shutter button half way the viewfinder image went all white for a short time and then it got to normal exposure again - what is that about? I tried to find settings to disable this flashing but wasn't able to. Also the outlines of objects were shown with jaggies (staircase like effect of pixels) where the steps move to different places as I turn the camera around even just a little. To me those artifacts are very distracting and I find it not possible to intepret the scene and human expressions in the presence of such moving artifacts. With the LCD I can live as it is such a small part of my visual field and I don't find the artifacts as bothersome when I can watch the subject with my eyes directly bypassing the camera. But using the back LCD wouldn't work for telephoto action photography due to stability concerns, and I think DX DSLRs will continue to have a large presence in that particular field of photography. The D500 viewfinder by the way seems larger, almost FX size due to its higher magnification, so even that argument is less of an issue today than it was 10-15 years ago. However, I do think Nikon ought to do a few DX fast wide angle primes to complete the lens portfolio available for DX DSLRs.
I tried out something interesting in the D5600. This camera and its predecessors have the option of using a part of the touch screen to move about the focus point, but by default this feature is disabled and can be accessed through reprogramming the touch screen Fn to select the focus point. After that it is a lot of fun to use, though I have to say that the D500's joystick is more responsive and precise than use of the touch screen of the D5600 for this purpose. I tried the D5600's Snapbridge, connecting to my iPhone 6 and after more than 30 minutes trying it out I wasn't able to get the two devices to establish pairing. It seems like it is a total joke, unfortunately. How is it possible that they market something like this that simply doesn't work and then advertise it as one of the main new features of the camera?
Otherwise the D5600 seemed like an excellent lightweight camera. The autofocus worked very well with the AF-P lens attached, and it was amazingly quiet. I was very pleased with the camera other than the Snapbridge thing; unlike the D5 you could use the touch screen to use the menu and select info screen features. It seemed far easier to use than the first D5x00 series camera which I tried a long time ago.