My fears were unfounded!
Microsoft Comments on UWP Games and Full Screen Capability
http://www.pcper.com/news/Graphics-Cards/Microsoft-Comments-UWP-Games-and-Full-Screen-Capability
One particular fear for some gamers is that Microsoft would attempt to move to the WDDM compositing model not just for games sold in the Windows Store, but for all games that run on the OS. I asked Microsoft directly:
To answer your question, can we assume that those full screen features that work today with DX12 will work in the future as well – yes.
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
Steam / Live / NNID : jonxiquet Add me if you want, but I'm a single player gamer.