To work they need hundreds of thousands, maybe millions of these things floating in a specified target area.
What's the plan?
Drop a dcp10's worth of this stuff from a plane and then hope the wind doesn't blow in the wrong direction?
The only way this weapon is more effective than a ballistic missile is that if it is already everywhere.
It's then just a question of programming active and inactive zones.
Problem is, that this is invasion.
Quadtrillions of nanites (wrong word. These things are the size of dust particles) floating through China and North Korea choosing not to attack because America is feeling Generous?
That'll go over real well.