So why haven't Apple already solved this? We can't know that for sure, secretive as Apple is. But I'll bet it has something to do with the new iteration of OS X.
Lion In Lion Apple is bringing iOS features back to the Mac. Specifically, for notifications, applications are now encouraged to be full screen. Full screen apps can't use badges or jumping icons in the dock to notify users of what's going on.
Lion has to redesign notifications. And Lion has to make notifications work with full screen apps, exactly the same problem that Apple faces on the iPhone and iPad.
Unified notification system I believe the new notification system will be the same, or very similar, across all Apple platforms. It just makes to much sense not to, all their devices need new notifications and they face the same constraints... Except input. iOS handles touch, OS X has a mouse/keyboard. Both of them handle gestures however.
Universal Gestures? In the new beta of iOS, 4.3, Apple has released a set of gestures to do multitasking making the feature a lot more powerful and easy to use.
These gestures don't translate all that well to the iPhone (five fingers on a 3" screen?) but I dare say Apple can solve that. But I also notice there's one gesture missing: down. Right and left swipes change app, swipe up to show active apps, why not swipe down to show a notification app/menu?
Notification app/menu/dock Gathers all notifications, only needs to make a sound or visual cue for new notifications and users can come back to it at will. It would work on all Apple devices and could be accessed by gesture or from the icon.
Sounds pretty Apple-y to me. What are your thoughts?