Been waiting for this to happen for ages.
Now, when they say that they took some out with an AA missile, how many missiles for how many drones? I'm guessing that it's a lot cheaper and more practical to launch 1000 drones than 1000 missiles, especially if you only need one to get through and your target doesn't HAVE 1000 missiles.
This is basically what first popped into my head when GPS + load-bearing drones became a possibility. Not even a professional attack, either. Amateur terrorism. Coming soon to a city centre near you. It's scary stuff.
Maybe then these things will get some regulation (but that won't stop them either).
Literally nothing stopping someone making an "art project" of 1000 drones in a warehouse, and then making them fly out... over thousands of kms if necessary, by all kinds of random routes. Landing on a building should they be low on battery, solar panel on the back and off you go again (maybe even with a little fuel for an "emergency" launch if it detects someone approaching / touching it while it's charging back up).
Program in the same target location to them all, their origin will basically be impossible to ascertain (quite why these one's origin was isn't explained), they would come at you from all angles, over the course of many hours (or could be synchronised to the second but likely to generate attention while they wait around) and you'll never be quite sure if the attack is over.
It only needs one to get through to cause havoc, it'll generate scary headlines IMMEDIATELY and have a massive knock-on effect, it won't need a ton of funding, or for them even to be carrying anything necessarily, and it'll be hard as hell to knock out 1000 drones all in a little flock that you can't just get with one missile.
I would also think that rather than bombs, gas would be more effective - much more scary, basically only needs some scary-looking green fogging gas to be heated up to prove proof of concept and scare the life out of everyone, lighter, controllable, doesn't make you explode while you're setting it up, etc. and yet still a viable attack method if you did have some dangerous gas.