Right, though for the "get another gun with it" goal, I'd think a simple suppressor would be a good idea to ensure you have time to deal with the other guy's sling/holster/whatever and make sure his gun is ready before his buddies come running to see what that shot was about. Something like a pen gun would be easier to conceal when suppressed, especially if built into (or to resemble) an innocuous object like a cane, crutch or flashlight.
3D printed suppressors?
Been done too.
https://www.youtube.com/watch?v=2UlOm5kGqAgDisadvantages would be durability obviously, and fine threads and concentricity with the bore. Presumably negated somewhat by the fact you're expecting it to be a relatively disposable item. Advantages of 3D printing are that it excels at making blind voids, and shapes that are impossible through traditional subtractive manufacturing. So in theory, you can make whatever kind of gonzo-crazy shape that's the perfect fluid-dynamics solution for the caliber and velocity you're trying to achieve.
Metal 3D printed/laser sintered suppressors have also been done as well.
I'm kind of thinking that as time goes on... "guns" are going to be the LEAST of the .gov's and sundry statist worries. What about printing anti aircraft missile parts? Mines? Artillery? Drugs? Chemical Warfare Agents? Real (biological) Viruses?
Hell, postulating zero "new" technology or materials science, just working with a snapshot of what we've got right now, Wii controllers, smartphones, Audrino and Raspberty Pi, it should be completely possible to design an open-source quadcopter drone killbot using off the shelf commercial parts. And there's probably a half-dozen ways it could be lethal without needing to procure or synthesize explosives.