Relatedly, XAML shares enough low level primitives with DirectX [0] that the interop story was always meant to be smoother and it is something of a shame that it has never been particularly smooth.

It was a massive lost opportunity in UWP that DirectX never released proper, first-party WinRT components. It's still almost criminally weird that DirectX still prefers ancient COM to WinRT. I partly understand it from a backwards compatibility perspective of support old games for the longest amount of time to not just move DirectX entirely to WinRT components, but WinRT was built for forward compatibility from COM and there are and have been Windows APIs with both COM and WinRT projections.

Some of it just seems stubbornness that DirectX isn't directly usable from WinRT (and/or that "second party" projects like XNA were murdered). Certainly another thing to add to the list of why Windows Phone 7/8/10 all failed to have half the catalog of games that other systems had. (There was some DirectX in 8 and 10, but only for C++ apps. It should have played way more ball with WPF and in languages like C#.)

[0] Far more than it shares with Win32, which is partly why some die hard Win32 programmers have always disliked XAML.