spraynpray: "I want them to have a strong and well thought-through product line that is clearly enough differentiated that each camera sells well to the segment it is designed to"
Tom Hogan agrees with you. He just thinks his proposal, which I quoted above does it better because when the Nikon 1 (and a new Nikon model he has suggested) is included he has "3 CX, 3 DX, and 3 FX: basically an entry, mid, and top in each line, with the lines being spaced nicely." Tom feels the current line up is "more hodge podge, with new/old overlap and essentially four choices in each category." By the way Tom also mentions a larger buffer should be put into the D7000 replacement and I agree. That shouldn't add much cost.
Tom notes: "I keep getting vague hints from anonymous sources that the D400 is indeed not a DX camera but something akin to a D700s." and "The interesting thing is that there are two missing cameras from Nikon's DSLR lineup: a high end DX model, and an entry level FX model." "[T]he D7000 is coming up due for an update late this year. Could it be the new high-end DX?"
I raised the same question here some time ago and many people "flamed" me for it. It is interesting to me that Tom is making a similar suggestion.
Tao: Yes, I have a D800 on order. Just too much camera for the money, too hard to resist for me. But I admit if a 24mp DX D400 were available for half the price I probably would have purchased it instead. Or if a 12/16mp FX were available for 2/3rds the price I probably would have purchased it. The problem, for me, is that neither of those two are available, or announced, so I don't know what they will be or when I can get one. I am looking for clean high ISO about two stops better than my D7000 when enlarged to the same size (not when viewed at 100%). I don't know if the D400 will give me this: maybe Nikon will focus on resolution as it did with the D3x rather than on speed like the D3s. Maybe the D400 will be the DX D3x and I don't want that. I fear if I don't get a D800 on order now they will be in very short supply for a year. If I wait for glowing reviews of actual production models thousands of other people who read those reviews will also be ordering a D800 and the wait will be a year. I understand a D700 is an option, especially if used prices fall to around $1,500, but I am hesitant to buy 2008 technology as my "top" camera. It is fun to have the latest technology, such as the ability to recognize faces, even though I am not sure how important it will be. I suspect I will like it, and other features, a lot and would regret not having them if I bought a used D700. I see NR is reporting a $500 price drop for the D700. Perhaps Nikon can keep it in the line up and "modernize" it by simply replacing some of the internal electronic parts but leave the sensor at 12mp to distinguish it from the D4? For example, they now put an Expeed 2 processor in and make money selling it for $2,200. How much more would an Expeed 3 processor cost Nikon over the Expeed 2? All old parts have a cost and all new parts have a cost but the incremental difference may not be much. Seeing that the D800 with all its new parts is only $3000 the incremental cost of replacing the old D700 internal electronics with new electronics produced for the D4 and D800 might not be that much of a difference. If Nikon spent $100 more to "modernize" the internal electronics without changing the sensor, would they have a viable D700s they could sell for $2,300 or $2,400? I am just suggesting it may not be too expensive for Nikon to offer both a top DX in the D400 and an entry level FX in a modernized D700s. Only Nikon knows production costs for such a thing. But I suspect a strong market exists for both. Look at the NR poll in which more than half the people want a D3s or D4 sensor in a D800 body and complain the D800 has too many megapixels. If they produced it Nikon would be careful to "decontent" such a product sufficient to force working pros to still want the D4.
shawno: It would be nice if Nikon told us where they were going in the future. But I suspect they cannot "promise" anything because their R&D can only tell them what they are working on and what looks like they can produce but cannot guarantee that in 4 years X, Y, or Z will be available. Nikon doesn't want to promise only to disappoint. Better to announce when you are ready to deliver. So we have to speculate.
I certainly admit it will be a big surprise if Nikon produces both a D400 DX and a new version of the D700 as an entry level FX. It would also be a big surprise if Nikon took the D7000 "professional" by adding certain features to the D7100 or if Nikon took the D400 into FX. I suspect, if any of these surprised occur, we will see them by the end of 2012. This should be a great year for Nikon and for us!
[later addition] Tom just added more discussion on the rationale for a FX D400 as he sees it. http://bythom.com/ It is interesting to me to follow this discussion. Soon we will see what Nikon does with the D400 and with the "entry level FX" concept. I keep thinking the simplest thing is to make the D400 a 24mp DX and to let used D700 bodies serve as the entry level FX. That is where the odds lie; but Nikon might choose differently.