When it comes to the actual manufacturing retooling will still be necessary. Retooling once to make many many reproductions. 3D printing is not strong enough to hold up to any substantial force.
3D printing = Long time...every time. If you are a manufacturer volume is your bread and butter.
As you said 3D printing is great for the test pieces...how many of those do you sell?
3D printing is not being used in manufacturing. It's being used to help design the pieces you manufacture.