Personally I really hope they don't drop the dGPU - it is a move by Apple that I really hate, but with the redesigned MacBook Pros but here are the reasons why:I doubt Apple will drop the dgpu, they have little reason to, in fact they have more reason to fit a dgpu into more models because the new ones are so much more efficient and produce less heat.
1 - The significantly thinner body will require a larger space for batteries (despite the Skylake efficiency), so the logic board has to be reduced.
2 - The heat output also has to be reduced due to the thinner body.
3 - If integrated graphics can reach around the performance of the previous dGPU, Apple will change it (even if they have to wait as they did with the 21.5" iMac). The Iris Pro 580 is more powerful than the R9 m370x in terms of TFLOPS.
4 - There is actually no suitable Pascal or Polaris mobile cards that are currently shipping. The 400-series cards currently available are rebrands of 300-series cards. The m470X is a rebrand of the m385X which would not be suitable given the new form factor and power/heat considerations. Nvidia have mobile 1000-series GPUs available right now.