A necessary step for Windows to survive as a consumer platform. It need to be able to compete on price and simply with Android and iOS. Windows 10 S not only makes it possible for MS to have a free edition of Windows, but it will hopefully increase the availability of UWP apps.
It is possible that Windows will become truly closed some day in the far future, but without UWP it will be almost gone before that could happen.
Right now a cheaper and simpler Windows experience that can be upgraded to an unlimited pro version is the best possible scenario. It might very well fail miserably, but if you want Windows to remain relevant you better hope it won’t!
I hope Epic starts to understand this and drops it misguided hate of UWP.