This development is not interesting for gun enthusiasts. It may be interesting for people who need to smuggle a gun past security (you still need to get the metal parts + cartridges through the detector). It's not that interesting for people with the skills, tools and smarts to build their own gun, nor is it for criminals who can (in most countries) quite simply acquire a gun from an illegal source. But it is very interesting for people who want to acquire a gun illegally, not necessarily because they want to use it for criminal purposes, but in case they want one to defend themselves but the gov't doesn't let them have one.
And for that purpose, you wouldn't really need something that can reliably fire 10.000 rounds. 6 reliable shots would already be a vast improvement over nothing at all. And given the progress already made on these printers, I'd say that printing and assembling such a gun by anyone may well be viable in a few years.