So now there's a new camera: the D810. Nikon has taken the D800 and made some smart improvements, but not being good enough was never the D800's problem.
I rarely, if ever, challenge what my D800 is capable of. For the most part my lenses simply aren't good enough to match its sensor, but I'm still waiting for Sigma to make the one that I really want. A replacement for my 60mm Macro from their high-end 'Art' line would be nice, although unlikely. Their 70mm Macro lens hasn't really caught on, despite its excellent quality.
There are many useful things that I could do with the price difference between a new D810 and what a used D800 could sell for. Some of them even involve photography – a new computer, a better monitor, maybe a Nikon 70-200/4. For that matter I've recently spent almost as much on paper and ink as I did on my 50/1.4G, so that's also an ongoing priority.
And the problem that the D800 does have, the one that the D810 doesn't solve: it's massive and costs a small fortune. Right now that's the price of having the best 135-format camera in existence, but the much smaller and cheaper competition is getting better faster than it is.