Just listing a possibility for anyone out there that still prefers the simplicity and power of Capture NX2 but is on a Mac and hence cannot upgrade to Yosemite as NX2 is not fully supported in it (without a bunch of hacking).
Apple still sell Mountain Lion OS X Server Single License version for $19.99, this can then be installed in Parallels or Fusion with NO hacking required, and hence you will be able to continue to use Capture NX2 if you so wish within a virtual machine. The Mountain Lion OS X Server is NOT available on the Apple Store online, you must call in to the Apple Store and order it manually, the product code is D6378Z/A.
The reason for needing OS X Server instead of the normal client version is that Apple will not allow you to install the client version in to virtual machines and they just power down. The client version can be used with considerable hacking, but personally I prefer to take photographs than spend hours hacking things together ;-)
This isn't about what to replace Capture NX2 with, we all know that this may have to eventually happen for everyone, but if you want to extend the use of it while being able to upgrade your main Mac OS then you now have a relatively cheap answer.
UPDATE: Despite initial promising work it was not possible to get the Capture NX2 to function under the OS X Server Am now going to try another avenue and will report back within the next few days.