For example, the only Nikon rectilinear wide angle lens that works behind a (9") port with full frame cameras is the 16-35mm f/4.
Adam, I shoot the 17-35 f2.8 all the time on my D800. I think your statement is a bit misleading, as there are lots of good options as good as the 16-35, although it is popular. There are also some prime lenses too that don't seem to get much play, but are much smaller and easier to work with.
I'm struggling to justify upgrading to the D850 as the biggest issue I have with the D800 is frame rate, weight and size. I much prefer cropped cameras for macro and actually find that the E-M1 MKII is a winner in that realm, but falls apart in dynamic range.