Mikey Campell of AppleInsider is doing a great summary of the different technology Apple has on its tool belt.
Apple’s invention proposes the installation of a mutual capacitance sensor in the architecture directly below a Touch ID fingerprint sensor. In such arrangements the capacitance between two electrodes can be measured to ascertain distance, which is then be translated to applied force and reflected appropriately via a graphical user interface. For example, as a user presses down on a Touch ID button, the mechanism compresses, bringing two sandwiched electrodes closer together, thereby increasing capacitance as a function of force.
The Home, Lock and Volume buttons are the only buttons that ever were on the iPhone. Part of the reason is because there was no technology available at the time to do something different in terms of hardware/software interaction.
Being hardware buttons, they have to rely on low-level commands that still have to work, even if the software is completely frozen. This is one of the reasons they could not be incorporated inside the screen technology itself as a special row of buttons that disappear when the screen is not lite. Imagine a frozen iPhone with this type of buttons that also do not work. You would have to wait until the battery is dead to reset the phone… Not practical.
Force Touch, or 3D Touch, is still in the realm of hardware buttons and they could replace the home button with a pressure-sensitive Touch ID. Mikey also explains that Apple could detect different forces and therefore launch the Notification screen when pressed more firmly.
Bonus features, no more gaps between the button and the glass panel, therefore another step in the waterproofing of the iPhone case. At the rate we are losing last century items from the upcoming iPhones, it will really but just a slate of aluminum and glass, no 3.5mm headphone jack, no buttons, only pure unapologetically aluminum and glass.