Just wait.
People have already played around with attaching guns to RC aircraft. Inevitably someone will strap some explosives or a gun to one and carry out some kind of attack somewhere. The day that happens, the regulators will care very much.
The question is how the heck are you really going to regulate a little piece of styrofoam with some propellers/motors/electronics attached to it? Sure you can write some regulations but what's the chance of actually being able to enforce anything?
I'm sure someone will try, but I think practicality will keep the idea of using a drone as a weapon at bay. The ones people are using now have short duration, limited range and a small payload. They are also pretty noisy.
In the case of the gun idea, you have basically one shot at it and accurately aiming from a wide angle lens likely tougher than it sounds. Even if your killer drone has multiple rounds in it, recoil will make semi, or full auto useless. I single action mode, by the time you get recovered from the first recoil and lined up for another shot, your intended victim is alerted and fled.
The explosive may be more practical, but the payload restriction means it has to be a small and light bomb. That means you have to get very close to be lethal. Likely your intended victim will hear you coming and run for cover. Sneaking up from behind in a noisy environment might be effective.
A third idea might be dropping a small bomb into a crowd. Would likely work as a terror weapon, but not much as an assassination weapon. More maiming than killing.
Then there is the issue of recovery. Are you going to try to recover the bomber and the rifle drone, or abandon it and potentially leave behind a wealth of forensic evidence? If you try to recover, how will you not be seen?
Like I said, it wouldn't surprise me if someone tries, but I think the idea of a killer drone is more novelty than practical.
