lots of things. Remember the Cartoon Network PR stunt where they placed DIY LED "signs" of characters from a show around Boston not long after the bombing there? What about the kid in Texas that was accused of bringing a bomb to show his teacher his DIY electronics Arduino project? What about the Mr Robot episode using a RPi?

Also, people putting these regulations in place are not normal people but people that think about how people might cause mayhem. None of the things I mentioned were real threats, but they very easily could have been is the point.