Here is a quote from the ID@XboX program FAQ:
" Can I use my retail Xbox One as a developer kit?
Not yet. For developers working on Universal Windows Apps, you’ll be able to test your games on a retail Xbox One sometime after the second half of 2015. Selling UWAs on Xbox One will come in 2016. "
Since it’s already 2016 this Microsoft FAQ is either totally outdated, or the UWA testing on retail Xbox One should be possible by now or at least very soon.
So any news on when UWAs will be a supported platform in UE4?!?