One small detail, one huge consequence...
I'm just going to say it, this is a product that doesn't even need to exist. In a similar configuration the Air is lighter and cheaper, for a few hundred more the 15" rMBP is more than twice as powerful in CPU and has 3x better Graphics performance.
Nothing about this device qualifies as Pro except the screen, but guess what you are driving all those pixels using an integrated GPU which means you can FORGET about any type of benefit from any application/game that uses hardware based graphics acceleration (Any Pro App).
On top of that you can look forward to a laggier and more jittery experience in everyday *basic* desktop usage given you are REALLY stretching the capabilities of that iGPU. I don't care what the numbers on paper state, the HD 4000 is not trully capable of delivering a PRO experience at Retina Resolution.
The added benefit of running any high end app that taxes the HD 4000 is that you will also get a significant reduction in CPU performance as the Intel chip will need to throttle down speeds based on thermal constraints since you are including everything on 1 chip (if the GPU is running at 100% the Dual Cores will never reach their full speed) Bravo... Bravo...