It is just a concept...but I don't think it is that great...For starters - the alert popup for "quick reply" is essentially going back to the old iOS notification system. That and the view is just slightly not wide enough, so it looks crappy leaving a small border of app icons below it showing. Why not build the action into notifications themselves? Add a small "action" button to the corner of the screen when a notification slides in at the top of the screen, if the user hits it an app can launch a small quick action widget to reply to the notification. Although having an easier app switching gesture would negate the usefulness of a modal popup..I'd rather just open messages and switch back quickly after that (Without having to double click the home button.)
There are so many other UX issues with this:
1. Widgets - what is the real advantage? Music controls look nice, but you have to double tap..which on the iPhone 5 is going to be slower than just opening the app and hitting pause (If you have music playing it is probably already cached in memory, so there is no delay in opening the app.) You don't get the benefit of glancable information either - if I want to see the weather I still have to double tap the icon. Also I have to actually find the icon. If I am on page three I still have to swipe to get back. Putting widgets in NC makes much more sense as they are accessible from any device state.
2. Settings "slide-in" view. Sounds like a cool idea, until you realize it would be super easy to accidentally open it. No longer can you simply swipe through app pages. Instead you have to make sure you don't land on the settings icon.
3. Settings icons - the uniformity looks nice...but with a 9x9 grid of settings adding color to add distinction would not be a bad idea.
4. Shelf - A singular shared storage place for files sounds nice and I hope they implement it, but not like this. If anything they should be getting away from this style. Not to mention what happens when I have more than 9 items? A simple "Finder" app that can organize and open files (even with a QuickLook kind of preview built in) would be way better and more usable. Maybe it could use a tag based file organization system rather than hierarchal folders.
Some good idea, but missed the mark on many points.