you shouldn't even be comparing bitcoin and gold because they have nothing in common and not in the same category for one to replace the other. bitcoin is a currency and gold is many things but not a currency. gold will remain as it is as long as it keeps its use cases which it will. and bitcoin, as a separate and entirely different thing will grow only as long as it is offering what it is suppose to, meaning a decentralized secure payment system that is censorship resistant.
I believe gold were once used as money/currency in the market being traded by mere merchants in buying stuffs until the invention of paper money that is backed by gold reserves. There are characteristics between gold and Bitcoin that is comparable but I agree with you in not comparing the two. Gold will be gold and stay as it is and Bitcoin will always be Bitcoin and function the way it is intended to be. Bitcoin will never replace gold's usage the same way gold to bitcoin. In addition, is it possible to see a nations currency be backed by Bitcoin reserved?