I "might" be tempted to forgo the D7100 and go straight to the D400 at $1,700. But, no way at $2,300+. And, I believe that to get what the D400 wanters want will cost closer to $2,500, if not more.
Oh, and I think that custom-design idea is terrific. Maybe it would take a few months to get your camera, and it would cost a lot more, but you could get exactly wnat you want. Maybe, rather than total customization, they could offer it in three different configurations, with three different price points.
Then again, Nikon would NEVER do this. They won't even give us a 70-200 f2.8 without VR for $1,500, like Canon does. It took them until a few months ago to give us a 70-200 f4 as an alternative to the insanely expensive f2.8 version, when Canon has had that lens for decades. Nikon doesn't do flexibility and choice.