I have the same problem as described in NUC5i5MYBE Power Switch Bypass |Intel Communities
In my case, I have a NUC5i3MYBE board, updated to BIOS Version MYBDW130.86A.0044, embedded inside an appliance that contains its own internal power supply. I'd like to disable the board's power switch pushbutton to allow complete boot-up upon powering the appliance as a whole. It's currently necessary to tap the NUC's on-board power switch after supplying power but that switch won't be accessible on a finished appliance.
I followed the suggested solution in the other question and checked the BIOS Power Sense and selected "Power On" from the After Power Failure menu in the tab's Secondary Power Settings pane. The only other option checked in that pane is PCIe ASPM Support. With those settings, the NUC still doesn't attempt to boot when powered until the button is pressed.
A wrinkle is that the NUC has FreeBSD 10.4 installed.