As we are in the realm of speculation, I might as well have my penny's worth.
I would like to see the D800 as a slimmed down D4. I would like 16MP (although I am very happy with 12.2MP) but I do think that the Exspeed 3 would be very useful as it has shown in the V1 for fantastic abitities. I would like dual cards and while I am really a stills person, I can see the vaule of having video behind lens that cost me more than most non professional video cameras. Inevitably in the electronic age, features are undated rapidly rather than in the film age and so while the D700 is only 2 years plus, electronics and technology have moved on.
What I really like about the D700 is the low light ability and any exhancement here would be really welcome.
I don't really need or want 36MP. There would have to be a trade off and it would likely be the low light capability.
Was at a wedding last week, in a dark church with multiple lighting, candles and daylight and the combination of the ColourRight to white balance and the high ISO of the D700, I shot without flash whereas the official photographer had flash on his Canon!! Enought said.