The D7100 is a very good camera, but it's missing some significant features found in a pro or pro-sumer body. The biggest gap I've seen is the AF system. The D7100 version of the CAM 3500 DX AF system only provides one focus point above f/5.6. The D600 has 15 cross sensors and 33 total sensors above f/5.6. It has 9 sensors at f/8 compared to just one for the D7100. To me, this shows an obvious plan to differentiate bodies with the AF system.
The other big gaps are the buffer and frame rate. You need to call those features advanced, and I expect to see a much better frame rate in the D400 - one about the same or better than the D300.
I'm still expecting a D400 announcement in late summer with delivery in October or November at a price point of $1799-1999. A pro level DX body could be very interesting if they wanted to go that route for wildlife photographers, but a D300 successor seems to be obvious and would be a big success.