the current reprap style uses all printed fittings for threaded rods. you could replace the horizontal rods with printed racks (http://www.thingiverse.com/thing:14537), but your xy precision would suffer. This is homemade, scrounged parts kinds of solutions. If you have access to a nice commercial printer, you can print everything but the electronics and steppers at very high quality. I don't think anyone prints conductive inks as part of the process. I think you can steal this inkjet print head (http://www.thingiverse.com/thing:5152) and incorporate it into an existing system without to much effort.

There's nothing standing in the way of starting with magnets and wires and a 3d printer for motors. you'd probably want some cleverly placed metal sleeves for heat dissipation.

The electronics might be really hard, but they might not. Lots of universities used to let EE students fab their own VLSI chips. I don't think it's outrageously hard, it's just toxic. a lot of this might be solved with cool inks. I know there have been a few printable electronics doctorates handed out over the years.

so.. not long. not long at all.

https://en.wikipedia.org/wiki/RepRap#Construction

fingers crossed they get there.