I don't think it's inevitable, but bitcoin can be audited and transferred immensely more easily than gold.

The fact that historically, foreign countries kept gold in vaults in the US, speaks to this.

Also, gold gets mined at a faster rate when its value goes up. In that sense, bitcoin is a "harder" money.

There's also the possibility of people mining gold from asteroids, which could destroy the scarcity and value of gold.