The design — which was fleshed out in great detail — was based on electric carts running on rails within the factory, “paving machines” that direct sunlight to melt lunar regolith, robotic strip miners for obtaining raw materials, and a solar cell “canopy” for powering it all. After 10 years, over 100,000 tons of lunar factory could be produced autonomously. The factory’s functions could then be hijacked for the benefit of human colonists, used to produce housing, products, and provide large quantities of solar power.
If similar self-replicating systems could be constructed on Earth, there would be little limit to the material plenty they could provide. Self-replicating factories could turn the vast empty badlands of Australia into lush gardens by pumping water from the oceans, self-replicating factories in the high Arctic could melt snow and create gigantic transparent domes suitable for habitation, and submersible automata in the seas could dredge sand from abiotic regions of the ocean floor and process it into gigantic platforms for human colonization.
By opening up such vast new regions of the Earth’s surface, talk of overpopulation and crowding would fall by the wayside for quite a few decades, with people realizing how much space there actually was all along. And once things really do get too crowded here on Earth, we can move to the Moon, Mars, and the asteroid belt, using the power of self-replicating robotics to create rotating space colonies suitable for housing trillions of people.
Self-replicating factories could reduce the costs of material goods close to that of food — the primary expenses would consist of raw materials, energy, and whatever small quantity of human oversight is necessary to keep an eye on the overall structure of things. By utilizing special, man-made “nutrients” for top-level functions (rare or exotic molecules such as custom-synthesized proteins) and the broadcast architecture — whereby derivative factories must receive affirmations from a central parent factory to continue self-replicating — such factories could be made safe by design.
With such abundance, humanity might actually shift from having a zero-sum perspective on a world to a positive-sum perspective. With medical tools and basic goods in ample supply, no one in the world would need to suffer from poverty or curable disease. The nature of human work would shift from manual drudgery and mind-numbing routine to more creative and personally fulfilling endeavors, like art, music, math, science, literature, and exploration.
For more details on the state of the art in self-replicating machines, see the Wikipedia entry, or the magnum opus on the topic, Kinematic Self-Replicating Machines by Robert A. Freitas.