I think that the media foundation extensions will be fun, as I may even introduce the functions from Windows 8 as opposed to just the ones new to 7. That would mean adding stuff like Direct3D 11-based video APIs. Though adding DX11.1+ features will be pointless if the drivers available for Vista can't use them. And getting WDDM 1.1+ drivers on Vista is going to be one difficult undertaking, but probably easier than porting WDDM 1.0 drivers to XDDM (Windows 2000 Display Driver Model).