Advances like these are often missed by mainstream science fiction writers. Asimov's robot series may be the best. His psycho-history is in the ballpark with some of this stuff.
And the "futurists" often miss the big breakthroughs. I have Alvin Toffler's 1975 book "Future Facts": 300 pages of gizmo's, but he totally missed the personal computer as we know it... and it came just years after his book.
A big note about all the DARPA work. If the technology gets exported to the asian mainland we will have to face it later in an adversarial way.
The exit valve of the conveyor tube was concealed in a tangle of vines and ruins a quarter of a mile beyond the factory. In a slot of rock at the base of the mountains the valve poked up like a nozzle. From ten yards away, it was invisible; the two men were almost on top of it before they noticed it.Every few moments, a pellet burst from the valve and shot up into the sky. The nozzle revolved and altered its angle of defection; each pellet was launched in a slightly varied trajectory.
"How far are they going?" Morrison wondered.
"Probably varies. It's distributing them at random." O'Neill advanced cautiously, but the mechanism took no notice of him. Plastered against the towering wall of rock was a crumpled pellet; by accident, the nozzle had released it directly at the mountainside. O'Neill climbed up, got it and jumped down.
The pellet was a smashed container of machinery, tiny metallic elements too minute to be analyzed without a microscope.
"Not a weapon," O'Neill said.
The cylinder had split. At first he couldn't tell if it had been the impact or deliberate internal mechanisms at work. From the rent, an ooze of metal bits was sliding. Squatting down, O'Neill examined them.
The bits were in motion. Microscopic machinery, smaller than ants, smaller than pins, working energetically, purposefully - constructing something that looked like a tiny rectangle of steel.
"They're building," O'Neill said, awed. He got up and prowled on. Off to the side, at the far edge of the gully, he came across a downed pellet far advanced on its construction. Apparently it had been released some time ago.
This one had made great enough progress to be identified. Minute as it was, the structure was familiar. The machinery was building a miniature replica of the demolished factory.
"Well," O'Neill said thoughtfully, "we're back where we started from. For better or worse ... I don't know."
"I guess they must be all over Earth by now," Morrison said, "landing everywhere and going to work."
A thought struck O'Neill. "Maybe some of them are geared for escape velocity. That would be neat - autofac networks throughout the whole universe."
Behind him, the nozzle continued to spurt out its torrent of metal seeds.