Aerial surveillance drones are well on the way to becoming part of every major law enforcement agency's arsenal. Once it becomes commonplace to have these devices hovering over protests and demonstrations capturing video (and perhaps electronic data) of the protesters, they will become obvious targets for counter-attacks.
I predict that in the course of the next five years during the course of a major protest at least one of these devices will be rendered inoperable by an aerial attack from a drone operated by pro-demonstration forces. One feasible low-tech method for the attack would be for a pro-demonstration drone festooned with hanging wires or chains to descend onto a police drone, thereby fouling its propellers. (Though not specifically predicted here, there's a good likelihood that injury will result from the combating drones falling from the sky).
(Credit to the young adult novel "Homeland" by Cory Doctorow for laying out a similar scenario.
Challenge Chris E Spurgeon to a bet on this prediction!