p.1 #1 · Using 3D printing to make custome accessories
With 3D printing making custom lens hood, grip, and many other accessories should be very simple, but how much it would cost compared to ready made ones, I have no idea.
p.1 #2 · Using 3D printing to make custome accessories
3D printing is still in its infancy. A 3D printer costs thousands. Not to mention you'd have to have someone design your lens hood and assume it'd be a perfect fit to the lens. It's not as simple as saying "make me a lens hood" and poof, its done. Maybe 10-15 years from now it will be.