This is just a tip:
Due to the conflicts of having dual GPUs (dGPU and iGPU) if I were to get a rMBP (Late 2016) I would go for the iGPU only model.
Now I know this may sound like a headache, but if the prices are right and the dGPU is good, then sure go for it, BUT, I have been looking at some of these eGPU Rigs and man I gotta say TB2/3 is gonna be sick for all of us if we still want to do PC gaming.
I mean you can get an eGPU box with two Titan 1080s and connect to your Mac Pro or rMBP all the way down to MacBook Air, TB2 looks ready and TB3 coming or already here too.
I don't quite know but if you could find a PCIe 3.0 expansion chassis that would be S(L)ICK for like 10 years!
Think about having an iGPU for web browsing having fun doing simple stuff, and then every one to two years, if you guys like getting 2 new NVIDIA gaming GPUs and plopping them in, going thru the configuration and drivers, and loading up.
Thing is this seems to be the future of GPUs, honestly they keep getting updated so quickly (like yearly).
But you could disconnect from the GPU power house and then go back to couch with just the iGPU, no bugs no GPU switching etc.
I'd go for the iGPU only... (unless the dGPU is just SICK or BOSS)
Laters...