It is not about what a 3D printer can print, but about what it can make. 3D printer is known for making objects out of thin air, using hundreds of materials.
The best thing with it is that whatever can be drawn, can also be made. Most items can be made with it. However, if the object is complicated, then it should rather be done by professionals. That should not stop someone who wants to learn how to make complicated objects from attempting to make them.
3D Printing is about turning a simple object that has been created with 3D modeling and CAD into something that can be touched, shown and presented to for instance investors. The things that are printable (makeable) in 2D can also be made in 3D, since technology that is capable of it is already existing.
It is possible to print anything with 3D printer, and using an existing template. The manufacturers are capable of providing templates about where it is possible to print even a broken part of a machinery.
What can be made with 3D printer is only limited with the imagination, and capabilities. If it is imagined, and designed with a 3D software, then it can be made with a 3D printer.