I just don't see the 3D printing thing becoming "household". The technically adept will adopt it and use it but most people are not that adept at using CAD or CAM programs, scanning, getting different pieces of hardware and software to work with each other. Also, I don't think the finished products will be as good as molded products. They won't have the same integrity. It may be fine for Christmas ornaments and knick-knacks but not a lot else.
It isn't the "light bulb". The advantages of the light bulb were quite obvious. It is more like the "paperless office" and everyone working online from home. Great idea but probably won't happen for most people. It does however remind me of Steve Jobs mom - "Why would I ever need a computer in my home?"
Speaking of the light bulb - did you know that the first electrical generating plant only operated at night? The only electrical devices were lights and you only needed them at night. The future is unpredictable.