It's a bit tangential, but the role of small disposable drones in warfare will only increase in the coming years. They're one of the more terrifying (non-WMD) weapons in terms of capabilities in my mind.
Cluster munitions are banned by some countries (notably not including the US, China, Russia and India) because they leave UXO that is likely to explode later, killing or maiming civilians.
Just like the other examples (e.g. machine guns), I don't see drone swarms getting banned. Slaughterbots will be a documentary one day.