There are some rumors that to celebrate iPhone's ten years' anniversary, there are a drastic innovation in iPhone 7 in 2017. This is chance for the companies to increase the number of iPhone that will be sold. For the recent iPhone, that demand actually still peaked, but it not obstructs Apple to make continuous improvement, especially when iPhones has one decades' anniversary.
In their long-term vision, iPhone will make whizbang splash that is proven by their materials of the body. It will be created by using block of glass and aluminum with few buttons, bumps, and holes. They also will take a step forward by adding OLED display that occupy most of the front of phone, even all of it by wrapping over its sides.
Moreover, the screen will be curved with an edge-to-edge screen. Surprisingly, the fingerprint technology is also added in that screen, so both the design and the authentication really developed. Furthermore, their body will be made from glass that enable it to do wireless charging.
So, with this kind of development, there are many rumors that mentioned this kind of developments are too much for iPhone 7, so it may for iPhone 8. As Kevin Krewel said, he suggested to apple for immediately launch the iPhone 8, to keep their position in the marketplaces