Gold and Bitcoin have their own segments. Gold investors are usually people who do not understand or are skeptical of cryptocurrency
But what will happen when the future generations who understand Bitcoin replace the people who do not understand Bitcoin
I don't really think you understand the main ideology and purpose of bitcoin. If you do, you will never say that bitcoin is gonna replace Gold. Bitcoin was not developed to be an investment entity but it was meant to be an alternate form of physical currency which has no central body controlling it and provide a peer to peer environment for people to transact business with lesser charges.
Bitcoin is whatever you make of it. It's owned by the people, so the people decide what it is used for, not the creator.
Bitcoin gives people the ability to be their own bank, to store their own value. So it is a store of value.
Gold is a store of value. If Bitcoin eventually is seen as a more convenient and accessible store of value then it is possible that Gold will lose market cap to Bitcoin.
This has happened historically when Silver became easier to transact with than Gold, and then it switched back to Gold when countries began moving to the Gold standard. We are now off the Gold standard.
Maybe we will move to the Bitcoin standard?