so we know the 6 introduced round edges. just to follow apple's format, i believe that the iphone 7 will continue with the round edge but more than likely be an evolution of the 6 series. i would say the ipad mini form factor is the perfect candidate for the iphone 7. round and wait for it, the chaumferred edge is going to make a comeback! yayyy. now even further, i predict that iphone 8 will be another major overhaul, think iphone 4 and iphone 6 releases. i would say the brick form factor will make a comeback and sapphire glass. Now this would be another game changer. original= round, metal 3G/S= round redesign, plastic 4/S= brick redesign, glass 5/S= brick redesign, aluminum, evolution of the 4 series 6/S= round redesign, aluminum 7/S= round redesign, aluminum, evolution of the 6 series 8/S= brick redesign, sapphire glass all around 9/S= brick redesign, sapphire glass, evolution of the 8 series
I'm predicting iPhone 7 will be the new iPhone 6. It will be another epic release/rollout/upgrade/killer iPhone.
Another possibility is liquidmetal casing. Essentially shatter resistant and you can even dribble it like a basketball #