I agree on Nikon getting away from the D400 line. Why would they at this point? Aren't there PLENTY of DX cameras available as is? I don't have sales figures...but much has changed in technology and trends since 2007/2008. More FFs have been introduced, more FX glass has been invented (I'm fairly certain), and mirrorless -- unfortunately --is making some noise.
I think Nikon has too many DSLRs in the pipeline as is. As a side note, Canon dropped the 1.3X format a few years back, correct? I don't see them bringing that back, and Canon continues to put their efforts in other sensor/body design technology. Never say never, but the dream D400 (along with a "true blue" predecessor to the much fabled D700) will, frankly, probably NEVER HAPPEN.
At least the noise levels, DR, and video has improved since the D300s -- at TWICE the resolution. Coupled with a lower price (by several hundred) and an excellent AF system, what is left to implement? A "pro body" build in a DX format? 12FPS? ISO capabilities to 512K? Enjoy your very-capable D7100.