Agreed. I'd be interested in a D3x as well--after the price on the used market becomes affordable, I'd like a D3s/D3x combo, speaking as a D1H/D1x/D200 user. Then again, a D700/D600 combo will probably be more affordable at any given time.
Looking at sample images, the D3x is maybe 1 stop behind the D600 in raw for noise at ISO 6400. Not bad. Still pretty good. But it doesn't have 12,800. I'm usually in need of the higher end of the ISO range, but my current crop of bodies tops out at 1600, several stops too slow at times. 12,800 would be perfect for low-light PJ. D1H/D200 are great up to ISO 800. So that would be a 4-stop gain.
Btw, the D3s, D600, and D4 were virtually identical at high ISO for a given image size when I compared them.