If you think about it long enough, you can understand Nikon's logic. We may not agree with it, and it may be depressing, but it makes some sense. Each of us may desire a very specific, custom tool for our specific needs, but Nikon makes product decisions based on real market data. And, they have probably concluded that there simply isn't enough of a market for a conventional D400DX camera to warrant the investment in R&D and production capacity. The "pro DX" camera was not created so amateurs could shoot sports and wildlife. It was created in a time of DX only, so that pros could shoot those, and other subjects, with a smaller, less expensive body.
Wildlife. Birds. Amateur Sports. That's it, that's the market. And, they are all conquerable (and even better) with FX, if you can afford big pro glass (like pros can). Everything else that a serious shooter can shoot, can be shot better with FX - especially since Nikon made a relatively small, and lightweight FX camera (D600). The DX sensor still has it's place in beginner and hobbiest bodies, because it's less expensive and the lenses are smaller, lighter, and less expensive, allowing Nikon to meet price points. But, the number of very serious amateur and professional shooters who are in the DX market is probably pretty small. Present company excluded, of course.