Basically, NX-D is just a tweaked version of View NX2 that has a few more functions and stores edits in a sidecar file (unlike Capture NX2 & ViewNX2, which don't). The interface is horrible and there's a host of features that were present in Capture NX2 but missing in NX-D -
link. Nikon have obviously ditched U-point Technology (developed by Nik Software and used in CNX2) because they'd have to pay Google to use it (Google bought Nik).
Capture NX2 will no longer be supported after the non-beta NX-D is released. That means CNX2 won't support new Nikon cameras or new Windows/Mac operating systems. It also means (probably) that CNX2 can't be installed on a new system because the product keys won't work if & when they switch the activation servers off.
CNX2 is a proper editor - NX-D isn't. What a shambles - Nikon have left loyal customers who paid for NX2 completely in the lurch.