You are putting the cart before the horses. The first question is "why would anyone buy it?", and if you don't give an excellent reason for that, you will not s

You are putting the cart before the horses. The first question is "why would anyone buy it?", and if you don't give an excellent reason for that, you will not see a 3D printer in everyone's home. And this makes your question about possible things as useless as a designer's contest (where most of the prizes are awarded for physically impossible designs).