Since windows uses a different bootloader than android, it would take more than just overwriting the software, they'd have to emulate secure efi on boot, I think. May be too difficult. Dual boot does sound sweet though.
The system image has leaked online, but there is no UEFI file so not yet possible go flash on Android M8, just re-flash a Windows M8. Its gotten quiet at XDA, dont know if we'll see anything until a GSM version goes global