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.
It doesn't really take much knowledge to set up an autonomous drone mission. It's not DJI-levels of consumer friendliness, but I know multiple people that made and fly their own drones, and it's not something you can't do with a few YouTube tutorials.
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.