Earliest possible 3-D printing, and effects?

Since it appears to be the rage these days, with even proposals of building rockets with it...

What were the limiting technologies? Lasers? Computers?

What is the earliest the hurdles could be overcome? (POD of your choice.)

What effect would earlier 3-D printing have? Frex, could it have been used to produce the *Corvette, with soy-based plastic panels? Would it simplify car production? A/c production? Anything else? Reduce the number of jobs? Increase the variety of car styling options (by making them cheaper & easier to switch)?

Could 3-D printing drastically reduce cost of production of consumer items?
 
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