Sorry guys, I'm still not getting it. This starting to sound like the first arguements against having a camera in a cell phone. Why would you want that? It can't be very good! I'm not saying a pop-up is very good, nor am I saying it's a necessity but it is convenient!
BTW, I just checked the side-by-side specs of the D500 and D300S. While the D500 has all the techno-wonder one would expect from a class-leading camera seven years newer – improved sensor (=mp+ISO+DR), buffer (duh, let's add $5 more memory) and spectacular AF – the viewfinder only increases from 0.94x to 1.0x and Nikon ditches the pop-up flash that was on the D300S.
Now my math and physics aren't as sharp as many here, so forgive me if I'm off here, but a D8xx viewfinder is "only" 0.7x magnification of a view that is 1.5x larger to begin with. Wouldn't that put it at about the same size, give or take as the D300S and D500? So I'm having a little trouble believing the arguement that Nikon had to trade-off pop-up flash for a significantly better viewfinder. While I recognize 1.0x will be an advantage over 0.94x, I can't imagine it's enough of a difference to ditch the pop-up.
My guess is that it was a price-point thing: Nikon chose not to increase the size of the top shell of the viewfinder by a few millimetres to accommodate both a (slightly) improved viewfinder (0.94x to 1.0x) and a pop-up. I still maintain, though, that this smells more of an "optics" decision to make the D500 "appear" more professional, even though most would agree it's not the camera that makes the pro (except for wanna-bes), but what one does with the camera.
Different strokes for different stokes, I guess (said scratching my head).