I saw an interesting demonstration by a local research center where they have shown a reconfigurable manufacturing line that included robotic manipulators, CNC machines and a 3D printer. The idea is that you order it to build something and it atumatically assigns jobs to the machines and assembles the end result (in this case a pen stand with your name on it, with a pen inside assembled & delivered to you by the multi machine assembly line with the wheeled robot shufling parts betwen machines.

Their longer term planes are much more grandiose, with a system that connect multiple factories with many machines each. You woul upload your project files and the system will assign manufacturing to the most suitable machines in the factories and handle all the part transfer between the factories and assembling, with the resulting product arriving to you all complete and packaged.

In this structure a 3D rpinter makes a lot of sense, you can use it to print parts for smaller orders & for bigger orders let the machine build a mold for injection molding. Also, you can use 3D printers to print parts to enhance the machines you already have to make fulfilling the order more efficient, like some special packaging tools or assembly jigs.

So 3D printing is not likely to replace factory mass production, but has the potential to enahnce it signifficantly & make it much more flexible.