Many people are writing me with the contention that "there will be no D400 (D300s replacement) because such a camera wouldn't be very distinguishable from an upgraded D7000."
Nonsense. Even with the D300s we have some clearly visible differences: TIFF support, better body build, buffer size, different autofocus sensor, shorter shutter lag/blackout times, faster frame rate, 10-pin release support, more direct buttons for common settings, multiple settings banks, and so on. While none of these things by themselves is a game changer, added together they make for a more responsive, hardier, easier to control camera.
The "D7000 replacement will be better than D300s" position some are arguing basically works this way: The D7000 and D300s replacements will both have the 24mp sensor, the D7000 will get boosts in buffer and frame rate, plus the D7000 already has some things the D300s doesn't, such as the 2016-pixel metering sensor. Further, their contention is that the D800, which should be above the D300s replacement, doesn't exactly have a lot of things the D300s doesn't already have.
While I'd be the first one to say that Nikon hasn't shown us recently that they have any truly new ideas in how to improve DSLRs--everything lately has been sensor upgrades, video, and small incremental changes--that doesn't mean that there aren't things that could be done to set a D300s replacement above a D7000 replacement.
If Nikon kept a purely incremental change mode going: higher pixel sensor, bigger buffer, faster frame rate, higher specified shutter, 91k dot metering sensor, 51-sensor f/8 focus system, uncompressed HDMI out for video, 1.2x and 5:4 crops, USB 3.0, and more.
If Nikon were being more evolved, to this you could add: built-in WiFi, built-in GPS, more bracketing sophistication, Live View histograms and focus peaking assist, and a few other obvious things that should be laying around in various development bins and that Nikon should have heard the requests for by now.
If Nikon were smart, programmability and other future-leaning technologies would make their way into the camera.
So I don't buy the notion that you can't differentiate a D7000 and D300s replacement. The question is whether Nikon can ;~). Gee, they've been doing this for six decades now and I don't think they're getting senile, so, yes, Nikon can make a D7000 and D300s replacement and differentiate them.
Thus, the question becomes more "should they?" As I've outlined in previous stories, I believe the answer to that is yes. From continuity, competitive, and unit volume standpoints, strong reasons exist to carry over a four model DX line.
One point I was trying to make in DX month was that Nikon seems to have gotten a bit lost in how to market CX, DX, and FX at the same time. DX is the value proposition. If you want a camera that performs at high frame rates with a high degree of precision and quality, without a D300s replacement in the lineup your choice is to plunk down a lot of bucks on a D4. A D400 would be a value proposition, just as the D300 was to the D3.
Even if Nikon doesn't really understand how to market DX, I think they understand that they need a full DX line of cameras. What I believe that they don't understand is that DX needs a full set of lenses.