Throw in the upcoming version of iOS, which is known as iOS 9, and you would more or less have a winner here. After all, we have yet to see an iPhone that fails, and neither have we seen any signs of iPhone fatigue setting in, as the handset does not seem to be a victim of its own success, although the “C” series of the iPhone in the past proved to be quite the flop, relatively speaking.
Force Touch was first introduced with the new Macbook, and in an iPhone, it should work in pretty much the same manner, as the screen figures out just how much pressure is applied by the finger, resulting in different actions, depending on the app at hand.