Gold and bitcoin are kinda complementary. Bitcoin strengths are golds weaknesses and golds strengths are bitcoins weakness. For example, gold is stable, whereas bitcoin is volatile, combining both is the best way forward for those who can afford it.
Bitcoin and gold are fundamentally different things. And bitcoin can never replace gold. Because the main idea of bitcoin is decentralization and the lack of physical value. So bitcoin can not be the basis of the world economy.