Probably the most future proof Z170 motherboard out there right now is the Gigabyte GA-Z170X-Designare. Yes, it is ATX, but it has two USB-C/TB3 ports, M.2, U.2, DDR4/4000 and a slew of PCIe slots, one of which is x4 for a PCIe SSD or the Alpine Ridge card (should it actually ship), 2 PCIe x16...