We've reached the point of what some observers call "sufficiency" in the mid- and higher-level cameras, for the needs of most people, for most of their photographic needs. But there still exists at least some segment of the camera-buying population that wants to have a camera, or a camera/lens pairing that brings as many advantages and capabilities as is possible.
I remember the time when Nikon pro cameras had 2.7 megapixel sensors. I bought both models, the D1 and D1h, used, and they were good cameras in their era, but the D2 series had vastly improved autofocusing capabilities, and an extraordinarily better, smaller, lighte battery, one that could shoot 3,500 frames, or more on a single charge: the D1 cameras were huge battery hogs, and you needed three batteries per day to be safe.
There's always a segment of people who want to be on the cutting edge. I think the 200-frame RAW buffer, in 14-bit capture mode, could be a huge positive for people who want to keep shooting when important action actually is happening in front of the camera...coastalconn's osprey dives, fish-capture action, and then subsequent take-off and fly-off with the captured fish: there's a really great example of when a 200-frame, full bit depth buffer (200 shots!) could be of HUGE value.
I have been working on a 29-frame RAW buffer with the D2x since 2005, and a 29-frame buffer on the D3x since mid-2013...occasionally, I hit that buffer limit. For somebody who has been using say the D7100 for wildlife--that camera gives what is it in full raw mode? ONE second's worth of firing? The D7200 is better....but again...it's a high-level consumer body, with all that entails. I agree, for most people a D5 or D500 is overkill, but there are also people who'll get some good use out a D5 or a D500..
The higher-level cameras serve as halo products, as statements of capability for the camera makers, that is also a factor. The leapfrogging must continue!