Windows 8 (Metro) apps provide some limited themability via css. You can change fonts, background colors etc.. I'm wondering if there is also a system wide themeing capability, like there was in Windows XP (via uxtheme.dll and .msstyles files)? So if in a couple of years, when Metro no longer looks modern, one could change the style of all apps, and give all buttons rounded corners for example. Or make everything look like the Holo theme (Android), or LCARS (the UI the computers use in Star Trek), to name some crazy examples.
Note I'm not looking for an official, documented capability - I'm pretty sure that doesn't exist. I'm wondering if there is anything I could hook into as a developer, like what uxtheme patching and Visual Style resource editing does for classic windows apps.