Imagine a future iPhone centered around mobile gaming. Press the home button down hard enough, and a joystick pops up right out of the device. This is the scenario pictured in the Apple patent application titled "Multi-function input device".
The home button would have two modes, button mode (left) and joystick mode. In button mode, the home button would be flush with the surface of the iPhone and act as normal. Joystick mode pushes the home button up, so it rests above the display surface. This converts the button into a full-fledged gaming control stick for the thumb.
As noted by Patently Apple, the concept would have to be designed to accomodate Touch ID circuitry. The fingerprint sensor system is not discussed in the patent application.
Now that a variety of MFi (Made For iOS) gaming controllers have already hit the market, it's not clear if Apple plans to make this home button joystick mode a reality. After all, many patents are filed that never see mass production. Additional moving parts in the home button could also present reliability issues as devices age and experience wear and tear.Many accessory manufacturers have offered solutions for gaming, trying to make the experience more tactile despite virtual controls on the iOS touch screen. Products such as the Fling joystick for iPad illustrate one way a control stick can be added to mobile devices.