cant see them releasing a d400 any time soon as the 300 is still selling well and they have just release the 700, if they release a 400 that could take sales away from the other 2 which could be bad for them possible a late 2010 release if the economy is on track to be normal again.
They will simply stop selling the D300. The decision between a D3/400 and a D700 has very little to do with the price of the body which is minimal. The fact is that you need a significant investment in top-quality FX glass. The move to FX basically entails the purchase of the 14-24, 24-70 and 70/80-200. There are cheaper alztenrtaives but then you end up with worse IQ than a good DX lens on a DX body.

