Upload & Sell: Off
I love the idea of a D400 but I am a doubter. First, the price will likely need to be a bit higher than what people can buy a D600 body for, so most of the hobby-snap shooters are going to get D600s without considering the performance advantages of a D400. That leaves a smaller number of the more serious photographers as the market for the D400 and these are the same people who Nikon has been chipping away for years now. They've had time to save and be frustrated so many have gone to D700s and D800s already. Considering the market, a D400 would probably be the lowest volume seller of the entire Nikon line. At least a low-volume camera like a D4 sells for a lot of money with concurrently higher profits, but they'd have to keep the price of a D400 as low as possible to keep it competitive, so the money isn't there.
Plus Nikon hasn't released any decent DX lenses recently, not even an updated 24/2.8 prime that would be very popular with serious togs, street shooters, students. They expect you to buy a FX 28/1.8 instead. And everything they have released has been plasticy consumer-grade and cheap feeling until you spend $1500.
Thom Hogan's whining about DX is perfectly logical and correct but it's been ignored for years now. I agree with his assessments, which unfortunately are gloomy about the wisdom of Nikon's management. Or maybe the entire Japanese camera industry that tends to ignore its best customers wholesale.
Face it, if you are a wildlife, sports photographer - or you simply want a solid professional body - Nikon wants you to get the D4 and the best fast glass, there will no longer be any bargains like the D300 used to be.
And if Nikon actually does make a D400, considering that the D800 and D600 both had uncommonly high quality control problems, would you really want to be the first on your block to get one? Heck I can afford a D800 but I don't need it ~ and given the QC issues, I don't want to risk getting a lemon that Nikon won't even service properly. Plus... they'll burden it with "professional" video and all the other feature creep they're known for. You already know that lean and mean is an alien concept to them.
If you're a serious shooter who likes the D300, what is the compelling reason to change? It's fast, solid, and reliable. Most people don't need more resolution or video - higher ISO and DR would be great but for 95% of the time the D300 isn't lacking. I've never had the camera limit me even though it's six years old. So why not just pick up another low milage D300 body for under $500 and use it for another few years?
Buying used is the best revenge against a surly, arrogant manufacturer and that's what Nikon deserves.
The D300 and D300s will probably be the last pro-grade DX bodies with an optical viewfinder. Next they'll probably make some D7500 with an EVF and video sockets hung all over it. Hope I am wrong.