One piece of technology that has been missing for a model year or two is the glass on glass touch panels that were used up to the iPhone 5 a few years ago. According to rumors, Apple might be going back to that for the Apple iPhone 7 as it was shipped a few samples from Corning and Asahi Glass companies.
There is only one real reason that Apple would go back to that technology and it has a lot to do with increased resolutions on the displays. According to one source, glass on glass gave more flexibility to increase overall resolution.
As the video world moves towards things like the 4k resolutions, smartphones, tables, desktop monitors and televisions are going to have to be able to keep up with the times. This could be Apple getting ready for that revolution as the Apple iPhone 7 is rumored to be coming with a 4k Ultra HD touch screen display.