The new mobile Pascal series is very, very impressive.
The mobile chips are now within 10% of their desktop counterparts and straight up twice as fast as their predecessors.
http://www.gamersnexus.net/news-pc/2563-nvidia-mobile-pascal-1080-benchmarks-and-overclocking
Meanwhile the Polaris 11 chip in the new rMBP is expected to perform on par with a GTX 960m which is literally off the charts now.
Razer managed to fit a GTX1060 into their 14" Blade and Apple could have easily fit one into the current rMBP chassis but clearly the quest for thinner devices swayed their decision into AMD's direction for lower power consumption, so we'll be getting outdated graphics hardware once again.
I am probably going to skip the dGPU option in the new rMBP and hope for eGPUs or new iMacs with the mobile GTX1070/GTX1080.