I think as a non "top flight" wildlife photographer that the D7100 matches both my capabilities and lenses and the exotic long pro lenses are out of my league. I have the 300mm f4 and a Sigma 50-500mm OS.
Time was a few years ago I managed to buy the 14-24/24-70 and 70-200mm to match my D700 and as I did a few weddings and lots of landscape work the set up suited me admirably. Than I got the wildlife bug and the costs that go with it, a DX body and a few long lenses. I have recently changed my outlook towards my photography due to circumstances and just enjoy my D800 and D7100 and in some ways feel I've "levelled". I think I've tamed my NAS which I thought may be untreatable and just enjoy my Nikon's.
I really hope the D400 is everything that one hopes for and I am sure Nikon won't let you down