There are lots of reasons it is going to be over $2k. For one, they can get it from the limited market that is not satisfied with the D7100. Building essentially a D4, but with faster data throughput, and more compact since the D400 probably would not have the extra space in the integrated grip, the D400 is not going to be cheap to make. The sensor would not be the off the shelf Toshiba sensor since it needs a great deal faster read paths than the current 24mpx, so cost will not be so cheap being a specialty item, not used in mass market cameras. There is very little difference in the specs proposed for the D400 than D4 except for grip and maybe a couple hundred difference in sensor price, offset by the more expensive AF system in the proposed D400. If it is in the low $2000's it will sell as well as they need it to, since much of the market has been satisfied by the really good D7100 in Dx and D600 and D800 in Fx. If it was "only $2000", I would be first in line for one. If $2400, I would have to sell my D7000 first and one of my unused lenses, but It would be worth it to me.
When new updates on lenses double in price, and cameras, to stay in the same price points as the models they replace are going to decidedly lightweight cheaper bodies, the estimates of $1500 just do not make any sense for a pro body. The D800 is strong but not a pro body. The most expensive part of pro cameras is the structure itself since the electronics is not much different. Throw in a new concept AF system where no other camera shares the development costs, $1500 is a non-starter and if Nikon figured that was all they could get for a pro body DX they would not even bother developing it. From the proposed specs very little would be shared with other cameras which further increases manufacturing costs and speeds the period over which development costs needed to be earned back. Canon has shown little interest in competing in IQ or they would not keep recycling obsolete sensors and piling on features which do not integrate well into the platform. If they could fix it, who believes they would have not bothered with doing something about the consistent model to model banding and high read noise of all their models? A D3200 has lower noise than any camera they ever made. Nikon has a difference niche focus and if a D400 ever comes out, it will not have a competing model to contend with. Nikon is not shy about asking for their price on limited market items. Is a 80-400 AF-S really costing 2x to manufacture than the D version? Mechanical systems do not drop in price the way electronics does, in fact it gets more expensive with time. Stan St Petersburg Russia