That might happen someday. It’s actually amazing to an old fart like me how much can now be downloaded and/or done one the internet today that would have been beyond science fiction when I was young. We take for granted amazing technology. If you went back to 1900 and told them what we take for granted today you’d be committed to an institution for the mentally insane and given a lobotomy.
Hello? Your Part's Not In Stock Here Or The Warehouse And On Back-Order... It'll Be Ready In 1 Hour!
Or be given a book deal by the Jules Verne society. 
I was just talking with a fellow geek yesterday about tech changes. I still remember being absolutely blown away in the 80’s when I saw my first mouse. The idea that you could just point at something on the screen and choose it rather than having to type out what you wanted was astonishing.
Imagine what 35 more years of technology advances will bring. The example I always use is the airplane. We went from the Wright Brothers’ primitive flying machine that barely wheezed itself across a 120 foot flight to the SR71 which could cross the entire country in an hour, in just over 60 years, and the pace of technology advancement continues to increase.
The next 30 years are going to be devastating economically thanks to technology, but when we come out the other side we will be living in a world that makes Star Trek look quaint. I suspect that even though we will be able to print car parts in our garages, we won’t need to because we will also be able to print almost anything else we need as well.
When I was in college in the '70s we wrote programs in Fortran, keypunched the commands into 80-column IBM cards, added the data in keypunched-card format, and ran them through optical readers. That was the only way to talk to the computer. The internet hadn’t been dreamed of… at least not by the average person… at that time.
Yeah, in my opinion printing some of your own car parts at home may well be doable in the future… if you can afford the printer cartridges!!! 
Hadn’t thought of that… Inkjet ink is one of the most expensive products in the world per ounce. It costs more per ounce than Dom Perrignon champagne!
Now imagine how much steel ink to print that ball joint is gonna cost!
(I remember punch cards. I also remember jerks tripping people carrying stacks of them and laughing as the cards went hopelessly out of order. This behavior alone made me grateful for the invention of the disk drive)
@“B.L.E” hit it on the head. 3D printing can build infrequently manufactured parts economically, but parts made by the thousands or millions will continue to be produced using the same mass production techniques they are fashioned with today.
It’s not like other mass production techniques aren’t evolving. Metal injection molding (MIM), lost foam investment casting, etc.
In 1974, I had just started work and my boss suggested I go out and take a look at something new called a word processor. He didn’t know if it was anything useful or not but said to take a look anyway. I came back saying holy cow, that’s a revolution. Then came computers. Its been a wild ride but I’d still rather have my ball joint made in a foundry.
Some Are Doubting That These 3-D Printers Will Be Practical For Mass Production. I’m Not Certain That Any Of Us Know With Certainty Where This Will Go. I’m Not Doubting Anything.
An opinion in the article says, “Through the years, factory floors have needed multiple machines, each designed for one specific job, from bolting to soldering to shaping parts. With his new invention, DeSimone imagines nothing less than a manufacturing revolution.”
" ‘Think about a place that has 100 of these machines – and what’s really cool is, as you change what products you want to make, you don’t have to change the factory floor,’ DeSimone said."
What the heck, think about a place with a thousand of them…
Also, since they can print multiple components of a unit, already assembled, that would speed production.
Also, I think that in the medical field where more body part replacement components are being used, and that are unique in dimensions to individuals, this will revolution the availability of man-made body parts. Think what could be done linking an already ordered MRI with a fast 3-D printer…
And the article says,"The speed and flexibility opens a wide range of possibilities.
" ‘Complex medical devices, whether it’s inside of your heart or your kneecap or your feet or your teeth or your ears,’ DeSimone said."
CSA
All processes have evolutionary changes. I wasn’t thinking about them, but revolutionary changes, like 3D printing in comparison to mass production techniques or macining custom replacement parts on a CNC machine.
Shop techs always say, if they designed it on paper, make it out of paper. Let me know when printers make steel parts.
3D printers have printed metal parts for years.
More On 3D Metal Printing…
CSA
Not to bend the subject a little but back when they still had car restoration shows and seminars, I remember seeing a booth where the guy was spraying on metal. It looked pretty neat actually like a plasma cutter only spraying a layer of metal instead to fill in rusted sheet metal. I suppose it was a little expensive or didn’t pan out in actual field use, but thought it was interesting.
I still maintain that we’re not really talking about large production quantities of printed stuff. That video reminded me that I had looked at a job with Minnesota Rubber (I think was the name). They made bazillions of different little plastic parts. I understand you can make one, but when you are talking bins and bins of the same part, I don’t think so. In my youth I worked in a air conditioning plant, a hand truck and foundry plant, and a can and bottle cap plant. I’m just not seeing how a printer would compete with a punch press. No doubt for the molds and dies and so on but mass production of millions of parts a day is another matter.
@bing, I don’t think anyone is suggesting that a 3D printer is a mass production machine. Several posts have suggested just the opposite, and agree with you.