, exoteric wrote

... one wonders if the next version of Windows* will do the same for desktop applications. Thoughts?

Yes, I think WinRT will be extended to desktop applications. I believe Microsoft focused on Metro apps first for the Win8 release because it was the most urgent one (tablets) while desktop apps already have an existing ecosystem. Now the focus is on bringing WinRT to the desktop so that these new apps can be integrated with the App store and communicate with other WinRT/Metro apps.