I agree with Stan as well except that the price points stated for theoretical D300 & D700 replacements set up a straw man. I also don't buy the theory that Nikon doesn't see any market segment for the semi-pro body. The D700 replacement costs $3000 and it's called D800. Nikon has done pretty well with sales on that camera.
The D300s replacement? I had been leaning toward the idea that there would be no D300 replacement, especially if the D600 came in in the $1600-$1900 range. The D7000 seemed to position itself between the D90 & D300 which does raise the question of Nikon trying to merge those lines. With a D600 at $2100 it looks like Nikon has left open slots in the lineup for a $1600-$1900 D400 and a $1100-$1300 D7200.
I don't know what the market size is for a D400 but I can guarantee that the answer for enthusiast bird photographers isn't D4, and it isn't D600. It might be D7000/D7200 but that's a compromise over the existing excellent D300s which only wants for a sensor upgrade, and points to a segment where Nikon has had considerable success in the past.