D610s and D750s are getting pretty cheap, especially grey market models. It seems like it will only be a few years until they can be had for less than a D7100, or by then, a D7200.
When that occurs, there will certainly be a market for the features on DX that the D7xxx line provides. However, there is also a market for a D400 or D9000 that Nikon does not seem to be filling. It stands to reason then that the D7xxx line days are numbered. The D7200 when it comes out may be the last or next to last model.
So what will the last model in the D7xxx line be?