Don't know, but it's been discussed publicly rather recently:

https://github.com/Microsoft/cppwinrt

https://msdn.microsoft.com/en-us/magazine/mt745094.aspx

"Teams within Microsoft are already starting to use C++/WinRT to build WinRT components for the OS itself."

Thanks, that part I already know.

My point was more about Blend, XAML tooling support and official integration into Visual Studio.

So, all the things that C++/CX has today, but C++/WinRT was still catching up when that information was made public.