There are various possibilities as to what a D700 replacement would have. Ideally it'd have the latest sensor from the D3s, which would mean the pixel count would remain unchanged but the low-light performance would improve by another stop or so.
Alternatively, Nikon will chase the high pixel count of the Canon 5D II, and basically produce a D3x type camera, and probably add video/whatever.
If a wait involves getting the D3s sensor, then this sounds like a sensible thing to do. If it involves a D3x sensor then hmm, maybe this wouldn't be so good an idea...