Brad Ellis has some interesting ideas and examples on how Apple could shift the iOS interface from top-oriented navigation bars to thumb-friendly cards and sheets sitting towards the bottom of the screen:
The navbar has been essential part of iOS since Apple released the first developer kit, and it has served us well. But it’s time to let go.
Let’s agree to stop sticking important buttons to the top of the screen. Better navigation is within reach.
I think Ellis is onto something here. After Apple Music and Apple Maps in iOS 10, I'd be surprised if we don't get more of these "reach navigation" redesigns in iOS 11 (which would also make sense if Apple is releasing an iPhone with a taller screen later this year).