Not everyone wants or needs a dGPU, as evidenced by the millions of people who already have laptops and desktops (Mac and PC) that do not have discrete graphics right now.
Granted, some of those who have a tower-based PC with an x16 PCIe slot have that option already, but adding a video card is an additional cost for those people should they decide that they need one to extend the life of their PC. Unless your workflow suddenly demands a GPU, I suspect those people will not do that. If they do, what are they going to buy to go in their $500-$600 PC? An NVIDIA 1050 is the only real economical option for that price range PC. The 1060 starts at $200, which is a third of the cost of that $600 PC, so I suspect it is a tough sale in that market.
What dGPU should Apple have used? I suspect there is no satisfying answer for members of this forum, because everyone wants something different. Guaranteed, it would have been an AMD GPU. It would also be soldered to the board, which would have made no one happy, especially those complaining about the UHD 630 solution.
For now, anyone purchasing a Mac mini retains the option of adding an discrete GPU down the road via an eGPU. My hope is that prices for eGPUs continue to come down and that solutions begin multiplying. The proliferation of eGPUs also helps the PC industry as Thunderbolt 3 become more prevalent and users who prefer a Windows-based laptop gain access to Thunderbolt 3 ports on even value priced laptops that do not contain a dGPU.
Intel has indicted that they are going to integrate the Thunderbolt 3 controller into the CPU at some point, which will make adding Thunderbolt 3 an even easier proposition. It is up to users and the industry to make sure that Intel follows though on this sooner, rather than later.
I have no problem with them offering the intel 630 as the 'standard', but it would have been awesome if they allowed us to choose an internal dGpu as an upgrade, just like they allow you to choose an i7, or a bigger SSD or ram. That's all.
As far as the eGpu goes, for me, since it work at all in Bootcamp (or it's a massive pain in the ass to get it to work) that's kind of deal killer for me.