I'd think people would get progressively more interested in shooting them the lower they're flying anyway

Yeah, the article is talking about delivery drones which will be over 100 feet unless it's delivering to you or your neighbor. Ones under 100 feet are much more likely to be toy or spy drones which are much more likely to be a nuisance or worse.

If it's out of range of a shotgun you are almost certainly breaking federal law by shooting at it. Conversely if it's within range of a shotgun you might get dragged through court by the FAA but I think you could likely win if you have the resources to burn.

But anyway if you aren't rich enough to laugh off half a decade of court costs then you probably shouldn't shoot at them at all.