There's been a huge amount written about the current trend towards flat UI design and a recent glut of speculative articles about how iOS 7 might look.
This is easily the best succinct summary of some of the current trends (removal of button chrome, cards, etc.) and their manifestation on iOS that I've seen so far:
The future of iOS design?
There's one part I don't agree with though:
Google and Facebook have led the charge recently for throwing design resources at their iOS apps and redesigning them in a beautiful, subtle and elegant manner. The idea that either of those wouldn’t have inside information about the direction of iOS 7's UI and styling is beyond belief and we can only assume that the similar route they have taken (away from Google’s completely-flat Android style) indicates the direction in which Apple is pushing.
I doubt anyone outside Apple has been given a preview of the new iOS 7 UI; perhaps I'm being naive - I guess if iOS 7 includes the frameless hamburger and back buttons we'll have our answer.