Maybe one day human would also have a way to create gold out of water and air (they are all electrons and neutrons/protons anyway). From this point of view, a man-made limitation that is followed by all the participants can provide much better security than a nature limitation which might be broken by technology advancement
Do you really think that when it becomes possible to create gold out of water and thin air as cheap as dirt, gold will lose its appeal and shine?
I don't know about appeal and shine, but I'm certain it will lose its value. Basic laws of economics tell you that when a limited resource suddenly becomes plentiful, it also becomes less valuable.