Do anyone considered that D300 is the only pro model produced outside of japan?
This it means that if nikon want to release something in the pro range soon the eartquake make the D400 the perfect candidate.
Moreover considering that now D300s is under pressure by D7000 that is outperforming it in many aspects.
So if I was Nikon manager in order to imporve sales, and keep interest on the brand highm, I will put all my R&D dept. efforts on the release of D400 soon.
This is the most logical choice standing the actual situation.
D300/D300s made in my country, Thailand.
If you have D300s & D7000 like me you will feel the D300s is a lot of better control, a lot better focus in a low light. (But AF-s is slower than D7000) That cameras really not the same market.
However I think D400 will be the ground breaking camera in 4 generation.
Then they can't put it early.