Media Center is a 10 foot interface. The others are not.
Can Zune software sync with any mp3 device? If so, then kill off Media Player. Redirect any DLL calls to Zune.
As far as Windows 8 requests...
.NET/WPF takes a more central role, moving more of the OS code to managed where possible
Removing more compatibility code. There's no reason to continue support for Win 9x applications
Required Internet connection with only basic drivers included on installation disc
Central place to find, buy, install, and uninstall applications (similar to Ubuntu's software center).
I say bring back the Program Manager to replace the Start Menu. Its app icon would be where the Start orb is now. Similar to your suggestion, it would a central app to find, install, uninstall, update, organize and launch apps. Commonly used apps would of
course be dragged to the taskbar. handle update notification and install/update progress like the iPhone, with little red badges and on-icon progress bars.