Well-known developer Steve Troton-Smith shared information on a not yet announced Apple Pencil of the second generation. It is expected that the new Apple stylus will be presented tomorrow, and one of its main features will be an additional multi-function button.
The developer does not specify exactly what would be an external button or mechanical touch. The only thing that is known is that it will be located on the side of the pen. However, the button should have a sufficiently broad functionality, which will change depending on the usage scenario.
For example, in a graphical editor with additional keys the user can quickly switch between the tools or context menu. There is a chance that key will take over and part of the usual gestures. In particular, when Apple Pencil 2 the process of moving the canvas may be somewhat simplified.
However, this is not all the features of a button. Most likely, the functions of the extra keys will vary from application to application.