I don't think it's a lull, I prefer to think of it as a spring cleaning. iOS 6 is great, but it has reached a visual saturation point, making it difficult to add more ideas.

Sometimes you need to step back in order to advance further. The Pentium 4 is a case in point.

I'm sure there will be ongoing refinement to the visual language, and will feel finished by the time iOS 7 ships. Then iOS 8 and 9 will be able to progressively layer new ideas into the new literal and metaphorical white space.