XDA user chad.pflughaupt has come up with his next-gen Windows Mobile UI concepts, shown below, which take a strongly minimal approach with lots of transparency and gray icons. While the concept may be a bit bland for some, the minimalists among us may appreciate the lack of clutter.
Today screen. Obviously very minimal.
Pressing the Windows flag brings up this menu. Obviously pressing All Programs shows all installed programs. One could edit this to skip the shortcut menu and go straight to the Start menu.
Notifications will happen like in Android, by dragging the taskbar down. Very minimal dialer with Slide 2 Answer type action