Jay Leno has actually talks about this aspect a lot. It used to be nearly impossible for him to get parts for all of his old cars in his collection, and now he can basically just 3D print whatever part he needs.
The toy industry is going to crash soon. Once you are able to 3D print figures and other stuff in color, there will be no reason to buy toys or figures, assuming the materials are cheap enough. Just download/pirate some schematics and you are good to go. Imagine being a kid in the near future, 3D printing any toy you want.
Sure and that will make things easier lowering the cost per unit and but still won't get the benefit of economies of scale. At the end of the day, if you get a printer to produce 10 parts per run, and you need 1000 parts per run to deliver to customers, you will still need 100 machines and every part you produce will cost the same.
Nowadays you can make injection molded parts with moving pieces using non compatible chemistry and once you're past design and machinery, price quickly craters to the point these parts effectively cost cents. This is something 3d printing will never be able to do- the only cost you get to dilute is part design and you get some savings on facility running costs, etc.
And as the technology gets better and more efficient, part price will come down and 3d printed products will be more feasible for a range of products, but you can't beat economies of scale for mass market consumer goods.
Some say there's a future for bespoke consumer goods, as in you go to the shop and you just don't buy the hair drier that's on the shelf, you get to chose the design and it gets printed on the spot. and the 3d printed parts get assembled with the entrails at the shop. And so on. Who knows, we'll see how things happen.
What forces are driving those blocks together? It does not look like that tank has recirculation, so I don't think they are agglomerating by density. They are just hollow plastic blocks. I don't even see magnets on them.