It would cost money, right?
That would be a good idea, but probably might backfire and create a huge black market for designs.
Are you able to share things you have downloaded? There would need to be a lot of enforcing to do. Wouldn't you also need a large amount of plastic though, or are we just talking new printing.($$$)
I could see this work with lego, selling blank minifigure parts for collectors to make what they choose.
And finally, is this basically a mold-making machine? Because the TJ guys might be onto something there.