I'd agree with Thom on most of that, although I don't think that Nikon has a grand strategy of up-selling customers from Coolpix to CX to DX to FX. I think that the missing products in CX (bodies, features, lenses) and DX (lenses) are there largely because Nikon can't make enough stuff fast enough. I suspect that they are having to make choices as to what new products they introduce and DX fell behind because they felt that they needed video, mirrorless and a stronger FX line more.
Not sure about the D600 rumor though. I still think a DX replacement for the D300 is likely to come first.