<<This has been discussed before but it can be both the 'flagship DX' camera and a 'middle class DX format D-SLR'.>>
Absolutely right and that's the point. The hierarchy of dSLR' s has changed dramatically over the last few years with previously thought of as entry or higher level consumer grade cameras encroaching on the higher level market. The D7000 started it and this has now provoked the launch of a DX "camera for all seasons" or nearly anyway, the D7100. This is similar in the FX range with a D600 doing so much of the D800 very well.
We probably will see a D400, but the gap between that and its nearest neighbour is lessening and perhaps potential buyers of a D400 may well be put off by what is liable to be its inevitably high price tag. The market for a semi-pro dSLR undoubtably still exists, but my feeling is that the gap is narrowing.