Remember when the V2 was announced and people were saying “what’s the point?” And I kept saying “zwave plus, zwave plus, zwave plus”?
We’ve got the same situation here, in that the V3 will be capable of supporting significantly better technical security features than the V2. It should be S2 certified for Z wave, although admittedly we still have to wait and see on that. And it will be zigbee 3.0 certified, although it won’t enforce all of the advanced security features on the zigbee side in order to allow for compatibility with legacy devices.
All of that gets into super technical details that you won’t notice necessarily on an every day basis, but it does mean that those who are concerned about security issues should find that the V3 scores notably higher on those factors than the V2.
For this reason alone, I think it’s justified in calling it a new generation.
A lot of people won’t care about the differences, particularly if they have already been operating a home automation network based on the previous generation, but I do think there are people who will care. 
FWIW