It's interesting to see everyones thoughts on this.
What I was thinking was that something like this would provide a simplified yet functional and strong desktop experience. As it is now, the separate Metro/Desktop interfaces feel sloppy and tacked on. It's nice to have the normal desktop there, but it is really cumbersome to have to switch back and forth between Metro and Desktop constantly.
Due to the direction Microsoft has taken with the Desktop, and it's current implementation, it wouldn't be needed at all if they gave Metro some sort of task bar and allowed you to open regular windowed apps there as well. Of course I'd imagine they would make it flow a bit more with Metro, rather than just slap on the Windows 7 task bar like I did.
It would come down to being a "normal" desktop experience and you would have your usual control over the desktop, but instead of desktop icons you would pin your programs/folders Metro style, and have access to the Metro apps/widgets.