I have already had a set of plastic gears 3D printed (non-sewing project) The fit was incredibly precise.
The metal can be done now, but it is still too expensive. The cost reductions will just take some time, but yes, we will be able to print parts in metal soon.
P.S. There is a free app for the android phone that will let you put an object on the table and take a series of photos of it from virtually every angle and then it produces a 3d .STL file (the 3D drawing that the printers use to make the object) so making an exact copy will only require someone with an unbroken part to do that process.
FYI