That's something I've been keeping an eye on too. Kaby Lake and even Coffee Lake only have HDMI 1.4 support in their iGPUs, however that is already enough for UHD. It's the 60Hz part for which you need extended support, or, like some ITX boards and the NUCs do it, an on-board chip to convert the DP signal to HDMI 2.0.
But all current 1151 Thin-mini boards (with DVI or DP) will already do UHD resolution to a display that supports it. I don't know anything about Bluray though, if that affects it in any way, perhaps HDCP 2.2 is needed and for that you do need HDMI 2.0a I believe. Your solution in that case would be a $30 "DP -> HDMI active converter", made by Club 3D. I forget if I'm allowed to link to shopping pages, so, I'll just let you google/amazon that manually.