Interesting little tidbit from Microsoft’s Build developer conference:
Updates helping you support the Fluent Design System, so you can create immersive, deeply engaging experiences with Microsoft’s updated design language. Now every organization can make beautiful solutions that empower your customers to do more. With UWP XAML Islands, you can access the more capable, flexible, powerful XAML controls regardless which UI stack you use – whether it’s Windows Forms, WPF, or native Win32.
It seems like Microsoft is giving developers of Win32 applications the option to add Fluent Design to their applications.