Right now you can do very short runs with 3D, because of cost and speed. But the key now is being able to prototype molds quickly. Long term, who knows how fast or cheap it will get.
Injection molding plastics or die cast metals would be hard to beat for speed or price. BUT you have to figure transportation costs and flexibility in too. EXPENSIVE to modify injection molds.
Very exciting stuff!
Good luck with your endeavor!