are you 100% sure that Vega is not a "iteration" of the GCN core and it's a new, ground up design?
I'm with you with the 1080Ti being the same(even 1080 and 1070 were very much similar). I read somewhere that there is a voltage limiter on the 1080Ti because the life expectancy of the card would be severely cut if you'd run the card 24/7 at max voltage.
god damn this wait is itchy.
Vega NCU is developed from ground up.
After 1:40 explains it.
If you go back few hundred pages (early January) in this thread you will find links and discussion.
Also can find some description here
http://www.anandtech.com/show/11002/the-amd-vega-gpu-architecture-teaser/2
And an graphic from one of the presentations why NCU is different than the GCN generation.