I don't think a notification screen is necessary, but I do like the idea of a three screen carousel. I would use the screen to the left as a place for double sized tiles. The start screen would have all square tiles, while the screen to the left would have all rectangular tiles. Developers could offer both options in apps. I think the rectangular ones would be really cool for some apps like twitter and weather for example. It would come loaded with pictures and calendar. It could even have the me tile scrolling notifications.
The screen to the right could stay the same and the three screens would be a carousel.