If the d800 is going the way of high iso I would hope for a better then d3s not the same. I agree though.
I want to see a dx (d400) with some d3s iso abilities. That would be a camera.
I can't imagine Nikon letting their D700 replacement actually have better ISO performance than the D3s, I mean, why would anybody spend twice as much on a D3s then? I know they are going to release the D4 at some point, but I'd have to believe ISO performance will probably fall somewhere between current D700 and D3s - which I think would be perfectly acceptable and welcome to the entry level FX community.
On the D300s replacement (presumably D400) it would be nice to see D700 level of ISO performance... I am quite content on DX, as a D90 shooter, I am quite anxiously waiting for the D400.