Even the difference of being able to play or rent a 3D cutter at work or through some service, or iterating something at home that you've made yourself, where the only real cost to it is your time spent having fun, is game changing.
But the average joe is unlikely to own a kiln either and unlikely to own any form of industrial pre+post-process. Disruptive manufacturing is my main interest as well as the new models of digital distribution. I believe the home will be an extremely limited means of production, but indeed a computer controlled plastic extruder (3D printer) will be an accessible technology many can own.
3d printing is firmly about the long tail. I don't see how a "killer app" could make much sense.
In the case of normal printing, the desktop printer didn't kill the rotary printing press, (althought the internet digital press may). Desktop printers and rotary printing presses exist for different use cases. Printing notes to red mark or travel tickets vs. a glossy magazine/newspaer. The relationship is akin to 3D printing plastic / injection moulded plastic and will likely have different use cases.