>> I keep hearing D400 should be a DX D4 as the opinion expressed.
Some want a DX D4. But I think most here just want a D300 body - basically nothing added or removed, 8fps, a sensor commensurate with even entry level cameras now (think D3200), and a few more pixels, whatever Nikon can deliver at 8fps.
The D300 has a rather noisy sensor. It was noisy when it was new, and it is very dated (and relatively much noisier) now. Most D400 advocates mainly just want a D7000 level sensor in their D300.
I don't think a D700, today, would cost over $3000. The sensor would be far, far cheaper than the original BOM price. In fact, there is nothing obvious in the D700 that costs more than the $1600 D300 guts, sensor aside. It's basically the identical camera, sans sensor. Given the tremendous reduction in sensor prices in the interim, the D700 should price out under $2000.
I also suspect Nikon made a LOT of money on whatever D700's they sold the past year or two as FX sensor yields have obviously improved and prices have come down.
Nikon never raised body prices like they raised lens prices so I don't see any evidence of your assertion in terms of actual market prices across the body lines. I think quite the opposite... Nikon has clearly shown that when it WANTS to deliver more for less, it can. And with the volumes it generates the basic technology of even the Pro body parts is getting commoditized. Nikon simply doesn't always want to do that.