One thing we might see more of in the future is drone-placed IEDs. Steal an Amazon delivery drone, mix up some home explosives and you're practically there. Drones remove one of the largest barriers to IED use, which is that people get shot when placing them. Drone + sniper rifle, sneakily deployed on tall buildings, would be effective for similar reasons.

Lastly, you know what suddenly becomes a lot more effective when you don't have to worry about getting killed by your own payload? Chemical weapons.