Now that the gun has been demonstrated to work, I'm sure there will be more interest and it will continue to grow. As one would expect, terminally stupid politicians have already come up with the idea of banning the download and printing of such devices.... we all know banning stuff is oh so effective. Unbelievable that people are dumb enough to keep voting for such morons.
Technically it's also illegal for me to make bombs, yet the recipes are literally perhaps a click away. Give that I have some technical background, I could likely surpass the Boston bombing if I wanted. The only thing stopping me is common humanity and sense, no piece of legislation or law enforcement agency effectively stands in my way.
So it will be with this, but for the time being this is still legal... with an FFL and complying with current ATF regulations. I imagine the next step will be adding a magazine of some sort, or perhaps some kind of derringer configuration until they can figure that out (making a reliable magazine is hard enough with traditional materials).
Ultimately this will advance legally or illegally regardless of legislation. As 3D printing technology matures, the demand on the criminal market for such untraceable guns will drive criminals to hire those with the knowledge to make them.
Of course, the federal government will likely try something hilariously stupid like licensing 3D printers or something. Screw the other benefits of the device, if it can be used to make scary things you can't have it!
One thing I'm curious about is if you could make a plastic knife with one of these. Given the tech, one would think you could design and build the perfect edge.