iOS 7 is putting every current iPhone app on notice. The visual changes to iOS 7's core functionality is so dramatic that it will make every other app look outdated. Like stayed out in the baking Sun in the middle of Summer for three weeks old. Your eyes won't be able to look at it.
Jacob Reed agrees with the fact that your favourite iPhone apps will have to change some elements and has cooked up some mock redesigns to imagine how an app like Twitter or Instagram or Facebook (and so on) would look like on iOS 7. After you see the "iOS 7 version" of an app, you can't look at ol' iOS 6 the same anymore.
Most of the changes are subtle, some are earth shifting, I think almost all make the current iPhone app design look dated. You can see more imagined redesigns of iPhone apps here. [iOS 7 Redesigns, Buzzfeed]