There are two reasons. First, Bitcoin is a non-credit currency ten times stronger than gold. So unless Bitcoin is replaced. Otherwise he must surpass gold. Second, Bitcoin is close to being the ideal non-credit currency, and it is basically impossible to have another non-credit currency beyond Bitcoin. Combine these two points and Bitcoin is bound to surpass gold
It can only happen if Bitcoin becomes the standard currency to trade within the future, which we all know will take a very long time to happen, then it will surpass gold. But if not so I'd say not yet because Bitcoin is a currency that has not yet stood the test of time (as in stood it's ground across the globe) and it's just used as currency by certain people, meaning that it's not accepted world wide and for it to surpass gold it has to be accepted first before that can happen.