My samsung phone has the fingerprint scanner in the side power button (the only location that makes sense, IMHO). Software should be able to read gestures from this same sensor, no?
edit: Sorry, thinking out loud. A quick Google search confirms that my phone already has this feature in settings. Unfortunately, the gesture is mapped to showing/hiding the notification panel, instead of screen scrolling.
With software detection of coherent scroll sliding, filtering out grip holds, bumps, and other irrelevant activity.
But noooo! Apple stuck a touch sensitive screen on a keyboard! No justice.