Apple has a grudge against physical buttons, especially the ones that take up too much space. The company has filed a patent that describes the design of a compact pivoting input device, which will significantly reduce the internal volume that a button takes.
Its not just space saving, though, this mechanism can offer programmable feedback. Such buttons can be provide different haptic feedback, configured by software, and will also be force-sensitive.
The patent gives the iPhone power button as an example, so thats likely the first use case, but it these devices can find other uses as well. Instead of just buttons, this can be used for toggles as well (and the iPhone has one of those on its side as well). There are many more potential uses too, say a super thin keyboard cover for the iPad.
The patent goes into excruciating detail of the operation, but basically the mechanism is similar to a speaker an electric coil surrounds a permanent magnet. When power is applied, it moves the magnet, providing haptic feedback.
The magnet itself doesnt move much just 10 microns or 0.01 mm but thats enough. Also, theres a pressure sensor at the bottom to register presses (and the force of the press as well).
Apple already transformed the Home button on the iPhone into a fixed capacitive sensor that relies on the Taptic Engine to provide the click sensation. Same for the touchpads on MacBooks. Those are fixed though, while these new mechanisms will move however slightly, which may have a major impact on the realism of the click.