if you open an image in NXD, then click > "open with", an option to open with NX2 is in that dropdown menu.
I have the most recent build of NX2, and when the RAW file is opened from NXD open with NX2, the Nikon D810 RAW file can be edited in NX2.
Very strange, but it works, oddly enough.
I have NX-D v1.0.3 and NX2 v2.4.7 and this is what happens
1. Open a D810 NEF in NX-D
2. Go to Image > Open With > Capture NX2
3. The D810 NEF opens in Capture NX2
Most of the NX2 controls aren't there though.
The Camera Settings section isn't there at all - so no WB, Picture Control or Noise Reduction.
Quick Fix section - Exposure Compensation slider is greyed out.
Camera & Lens Corrections section - there's no Moire, Auto Distortion, Auto Red-Eye or Vignette Control.