Seeedstudio has something like this already, from a limited parts supply.
A couple of notes, pick and place machines already exist. They take components and install them onto a board. Then automated soldering stations also exist, either using wave solder or IR.
The biggest issue with this type of thing is that each new component needs to be entered into the pick and place. Many components are easy, since most surface mount caps and resistors are basically identical. However, once you move away from a few of the standard packages, every part is different and requires someone to enter the information (correctly) into the pick and place.
As for 3D printing circuit boards, many researchers are already working on this. I believe the technology is moving towards actually being usable, but there are non-trivial problems with such things.