They still might not be a real threat, though. Perhaps you and Abekkus would like to register a wager with the Long Now prediction registry and betting site? http://longbets.org/
Is an individual soldier not an autonomous weapon? Autonomy in war is an unchangeable given, not something to be (or that can be) overcome.
Talking about "autonomous weapons" as something to "overcome" seems like anti-AI fear-mongering. There doesn't seem to be any real basis for it other than assuming as a foregone conclusion that AI is necessarily prone to inhumane malice. I'm vastly more afraid of most humans having weapons than I am of AI having weapons.
I don't think it's as clean a division as you suggest.
Imagine somebody takes a drone platform with decent processing power, mounts a gun like that, and builds in basic target-seeking. Then they make 100 of those and turn them loose in a major metropolitan area. They'd fit neatly into a box truck and cost under $100k in parts.
It might not be as deadly as 100 people with guns, but logistically it's a hell of a lot easier and cheaper, and I'd expect it to have a higher terror value. Especially if you have them mostly land on rooftops and wait for a random period.
That's reasonably doable given current tech. And we expect a lot of progress in ML and robotics over the next decade. Imagine ones that listen for police radio frequency use and then very accurately target people in uniform, for example. Ones that can wait days or weeks outside charging. Ones that collaborate to map, track, and overcome threats.
Personally I'm not particularly worried about it. America already has a lot of weapons and explosives sloshing around; I expect we'll figure out how to deal with this too. But I do expect we'll have to deal with it. Too much of our existing defense is tuned for humans. E.g., fences and walls have been an important part of defense technology for at least 10,000 years.
They still might not be a real threat, though. Perhaps you and Abekkus would like to register a wager with the Long Now prediction registry and betting site? http://longbets.org/