Not much. Autonomous targeting and control are quite new and currently take a fair bit of knowledge and skill to get right, but I expect those barriers to lower

Not much. Autonomous targeting and control are quite new and currently take a fair bit of knowledge and skill to get right, but I expect those barriers to lower dramatically in the coming years. There might be power issues with such a long delay, but I'm not sure. I think the main drawback once this tech gets slightly more widespread is that most people who want to terrorize cities don't want to wait a year or two to do it. For long running conflicts (Israel vs Iran for example) I expect we'll see some fascinating and horrifying attacks in the near to medium term. Of course anti-drone tech is also evolving quickly and I expect that to continue so the shelf life of any specific attack will probably continue to be rather short.