A classic manual Bridgeport mill, a foundry for making castings, a heat-treating furnace, a steel planer, a lathe, a drill press, a grinder, and a supply of steel is enough for a master machinist to reproduce all that. That's what was used to make machine tools in the first half of the 20th century.
Now that CNC mills get more affordable, people are starting to get vocal about their visions of a self-milling CNC mill. :-)