Need something to do with a Z170 motherboard's numerous PCIe lanes? Asus' USB 3.1 UPD (for USB Power Delivery) Panel could be a useful addition to a case.
The USB 3.1 UPD Panel provides two USB 3.1 Type-C ports, one of which can deliver up to 100W of charging power for devices that support the UPD 2.0 standard. That power comes from a pair of Molex connections on the back of the unit. Communication with the host PC happens over a bundled SATA Express cable.
For systems with no open 5.25" bays, not all is lost. The USB 3.1 UPD's case can be opened to reveal a PCIe expansion card, which can then be inserted into an open PCIe slot. The card still needs to be connected to a SATA Express port to function, though, according to the manual. We've contacted Asus for pricing and availability info.