As reported by NikonRumors, Nikon Europe stated in response to a DPReview user inquiry that the D7100 was not intended to replace the D300S as the flagship DX model, notwithstanding what is stated on Nikon USA's website. NikonRumors also pointed out that the D7100 does not qualify as a primary camera for NPS (Nikon Professional Services). To me, this means there will probably be a true D300/D300S replacement - the Nikon D400. This makes sense because Canon's 7D Mark II is reportedly going to be priced in the $2000 range, presumably with features to match, which gives Nikon room to create an equivalent competitor.
If indeed there is a D400, what can we expect? The D7100 seems to have almost everything and is already far ahead of the D300S on most features.
I think the D400 is to the D7100 what the D600 or D800 is to the D4. The D600 is a very capable camera but it is missing the mark slightly on a few things such as a pro-grade AF system. The D800 also has nearly every feature a pro would want and has a very high 36mp resolution, but because the resolution is so high, it is not a fast camera, which makes it unsuitable for some pros such as sports, wildlife, or arguably even event photographers. Meanwhile, the D4 has less resolution than the D600 or D800 but does have everything pros could want in a body.
The D7100 does have nearly everything, but there is still room for a D400 to improve on it. Here are some features that are missing from the D7100 and that may be offered by the D400:
1. Full magnesium body. The D7100 does have a magnesium frame and full weather sealing but the magnesium doesn't cover the front. Here is what the D7100 frame looks like:
|image by Nikon USA|
|image by Nikon Imaging|
3. Dedicated AF-ON button.
4. Continuous shooting buffer. The D7100's buffer fills up very quickly (just 7 raw shots in 12-bit lossless compressed mode), therefore it might not be the best camera for sports or wildlife. I expect the D400 to have a larger buffer, or one that can sustain continuous shooting for a longer period.
5. Continuous shutter speed. The D7100 is already reasonably fast at 6fps, going to 7fps in 1.3x crop mode. However the D300S went as high as 8fps with the grip. Nikon usually doesn't take any step backward for newer models, therefore I would expect the D400 to have at least 7fps/8fps with grip.
6. Lower resolution? I would not at all be surprised if the D400 had a lower resolution of 16 or 20mp because that is one way the buffer and continuous shooting speed could be improved.
7. Slightly better high ISO performance?
8. 9-shot bracketing.
9. PC Sync.
10. Pro-style controls. The D300S had pro-style controls with the triple button arrangement (WB/Qual/ISO). The D400 can't have a 3-button arrangement like the D4 because it doesn't have the buttons below the LCD screen. Instead I expect it to have the 4-button arrangement like the D800 (WB/Qual/Bkt/ISO). I expect that it won't have a D600/D7000/D7100 style U1 and U2 mode and will instead have shooting banks (yuck). And no we probably won't find the green auto mode or scene modes :)
11. Headphone jack. The D7100 has an external mic jack but not a headphone jack.
12. A few more options, including the option to specify whether exposure compensation affects flash exposure (like the D4 and D600).
13. Built-in GPS or wi-fi?
14. May use a CF/SD combination instead of dual SD cards.
15. D4-style video capability.
16. Price: $1700, same as the D300S.
As for me, I rarely use continuous shooting so I'm happy with the D7100 specs as is, and the extra features aren't worth the extra $500. For many pros however, I could see the D400 as being worth the extra cost.
If you are interested in the Nikon D7100, you can join the Nikon D7100 group on Flickr for discussions and samples from the D7100. I will be posting there regularly.