Add a wireless display has *never* shown under 8.1, before I removed the widi software package some extend display actions would launch the widi app which would complain its not compatible with my OS. I do not trust the source of the information but someone had written that miracast is a licensed product your oem had to include in the OS when installed on your device.
The drivers look good. I had gone and displayed hidden devices and cleaned out all the erroneous legacy devices.
I did not add wireless software extensions.
I do not know if the 750M can be fully disabled, but in win8 w/widi it was working fine as-is.