This is the thing. I'd like to create two .VHDs (Win 8.1 and Win 10) - for Native boot on Surface Pro 3. There seems to be some issue getting Win 8.1 VHDs to work on Surface Pro 3 as pointed out here.
http://www.wikiguga.com/topic/2570ea971d65571f8ca9f7d8b81167fe
Surface Pro 3 Boot to VHD...