Keep in mind not all industries need large volume
3D Printing will never come close to replacing mass production, but for low volume operations it "can" be more cost effective. And low volume doesn't necessarily mean "niche industry". Aircraft are only produced in lots of hundreds to thousands. If you have a single part that is expensive to manufacture for an aircraft by traditional methods then producing this by 3D Printing might be cheaper. The Space industry is another which can benefit hugely from 3D Printing.
3D print parts can be far more effective/efficient then many traditional parts, because you can build in a single part things which would take multiple parts in traditional manufacturing (think internal cooling channels, etc.). However, the technology is not really there yet except for on a very limited number of parts. The time for production of metallic 3D parts is still too high, and the cost/part analysis really only works on extremely short volume runs at the moment. 3D metallic parts also require significant amounts of post work machining (surface finishes, hole punching, thread tapping, support material removal, etc), so they will never replace the traditional workshop.
Still the metal 3D printing industry does hold some promise, just forget about it for mass production - areas like Space, Aero, Medical and custom engineering jobs can all benefit. Auto and consumer goods - not a chance!