My wishlist is rather mundane. I'm still using the D800E and am thinking I might skip the D810. But, that said...
A small resolution bump wouldn't hurt, say to 45MP.
Minor improvements to the color filters - the transition to red is a bit steep. Not surprising due to the higher sensitivity at the red/IR end, so it's a tradeoff between ISO sensitivity and overall spectral balancing away from red. I would prefer it not to light up in the reds quite so easily and would happily trade off ISO sensitivity. It makes things like red fall leaves look brilliant, but blotches up human skin and makes other kinds of subjects capture poorly.
Facial recognition, tracking, and automatic AF point selection. Light up the AF point so I can see what it's tracking. I shoot a lot of talking heads, and this would be convenient. Even better, eye recognition with a facial fallback. Maybe two auto eye modes: close-in where an AF point fits on the actual eyeball, and one where focus ends up on the brow - in the latter case, auto adjust focus backwards a point or two to approximately shift it to the eye even if the brow is what's tracked.
Let me switch between faces or eyes with the thumb dial/stick/controls.
Add animal facial/head recognition.
Let me engage the crop frames in the viewfinder without cropping the raw image. The JPEG can be stored cropped to reflect the viewfinder frame.
More sizing options for small JPEGs.
But this is all in the "convenience" category...