The short answer is yes we are going to see a Nikon D400 simply because it is a number that fits in well with what Nikon already have a model names like D600, D700 and D800.
What may come as surprise (my guess) is that is going to be something completely different than people expects.
At the moment people are expecting an upgrade for D300s which is way overdue. Got a nasty surprise a couple of days ago where I visited Nikons web-site and saw that you are still able to buy it. Wonder if there are even selling those anymore. Why not go for the D7000 if you are going to buy an advanced DX camera?
Well the D400 has been a wishing camera upgrade for advanced DX users for several years and Nikon has nothing to show for it. My guess is that many of them now are moving on to FX which just might what Nikon wants. Some have taken the D800 where you get a D7000 mp DX camera inside if you need that and then you still have the FX feature. Others are hoping on to the D600 wagon and seeing what a wonderful camera this is.
Yes there will an upgrade for D7000/D300/D300s next year (2013) some time early summer or late spring. Why not before. Well they want all you advance DX users to buy a D600 or D800 because there are more money in it for them as they get to upgrade your lens collection to.
The D400 will in 2013/2014 be the new entry level FX camera when the sales of D600 and D800 is going down. Just look at the numbers. In DX they are going for D3xxx, D5xxx and D7xxx and in FX they have the D8xx and the D6xx. Do you see a pattern?
My guess for the year 2013 in DSLR from Nikon is called:
- D7100 the most advanced DX camera (most likely spring time)
- D400 entry FX model (most likely late autumn)
- D4X medium format FX camera (not sure about this one)
And a surprise might be a D1000 as the first mirrorless DX camera...