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.

Anyone who has experience with 3D printing?

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.