Stronger iPhone 6s Design
The iPhone 6s and iPhone 6s Plus probably won't have a redesign though we've learned that there could be at least one substantial addition to Apple's all-metal design from last year.
The iPhone 6 feature Series 6000 aluminum. This is an extremely common material though it comes with a weak point. This weak point was exposed during the Bendgate debacle that arose shortly after the iPhone 6 release in September.
To squash this issue, Apple will apparently use a new Series 7000 Aluminum, the same material it uses with the Apple Watch Sport. This should protect it against bending and it should also change the dimensions of the phone a little bit.