There is a nice talk about it, somewhere on YouTube.
Then there was the whole 8.0, 8.1 with UAP, and finally UWP transitions.
The two only good things from UWP for .NET devs were finally getting .NET Native, which should be there since 1.0 given the Delphi roots of Anders, and the COM Runtime model that was in the genesis of .NET (formerly known as Ext-VOS).
I think the talk you refer to, is one from OS research group at MSR.
UWP/UAP is a new UI stack from the Windows team BOUND to a CoreCLR. That is different with the existing .NET UI technology stacks.
Additional, the CoreCLR and its more modern Assembly packaging (System.Runtime vs mscorlib) made the code difficult to share (recompile or PCL). This is solved now by the .NET Standard.
Which is what I meant with "mess created by Sinofsky regarding .NET, UWP and C++/CX.". I do have UWP experience since WP 8.
Thanks for the link about the talk.