Win 8 uses two runtime APIs, the regular WinAPI, and a newer WinRT. As it is known, Win 8 starts along a new path with it's Metro UI, designed mainly for portable (touchscreen) devices, which is very frustrating for some desktop users. Win 8 also provides a conventional desktop beside the new Metro UI.
However (!) an application written in WinAPI cannot appear on the Metro "desktop", while WinRT applications will not function as window applications on the conventional desktop. That is because Metro does not have windows the way we are used to them.
WinRT applications can run hidden (services mostly), run as a tile on the Metro UI, run in reduced mode (hardcoded 25% width of the screen), large mode (the remaining 75% of the screen, if another app is shown in reduced), and fullscreen mode. These are the only types of "windows" WinRT applications are allowed to have. This naturally incorporates a somewhat different "windowing" API incorporated into WinRT.
Microsoft does not hide the fact that Win 8 is a transiitional OS, and they intend to remove WinAPI and the old dekstop from Win 9. Win 8 only keeps this duality to give the developers some time to rewrite their apps to WinRT.
Thus a windowing system like SFML could provide functions through sf::Window, whether the application is forced (or put) into any of these modes and redraw the contents accordingly.
Recently I had to reinstall my computer, and I gave the Consumer Preview a try, and it really convinced me that this will be a good thing. VS2011 along with Microsoft Blend is a REALLY AWESOME IDE. Metro UI is practically based on HTML5, and therefore all application GUIs must be created in HTML5. Blend is a WYSIWYG HTML5 editor of Microsoft, and now it is integrated into VS2011, meaning one can import/export/transport Blend and VS2011 projects into one another. One can create a GUI, export it to VS2011 and get a bunch of handles to buttons, scrollbars or whatever that only need to be filled with C++ code, or just the other way around.
The only reason I uninstalled Win8 and reverted to Win7, was because I couldn't compile SFML, not even with 1 hour of messing, and my diploma thesis is more important, which is built on top of SFML. Once I hand it in, I might mess with it again.
Anyhow, SFML could provide a simple wrapping Metro "windows" for those who do not feel up to the task of learning a new runtime API.