You may need to go mini-STX ("5x5") for this. I've been Amazon-searching "z170 mini itx" and not finding anything that supports NGFF 2280 modules yet; however, if you have the case room for it, a low-profile riser that plugs into the PCIe slot will work.
Whew. Good to hear because I've got that motherboard on order.
Still not sure whether to get the Samsung 950 Pro now, or wait to see if prices drop and/or a competing model is released for a lower price. I'm inclined to NOT wait because it's going to be a tiny ITX build and to install an M.2 on that mobo later requires (almost?) complete disassembly of the system.