Both bitcoin and gold rest on the exact same premise: that, at some point, the fiat currencies (particularly the USD) will be hyper inflated to worthlessness. At that point, an alternative currency will be needed.
The total value of this alternative currency(ies) would need to be roughly the same as the current value (ie purchasing power) of the world's financial assets. If that is, say, 200 trillion dollars then the price of this currency(ies) will rise such that the market cap will equate to this equivalent purchasing power.
If we assumed bitcoin and gold were the only two alternatives and the market valued them equally then bitcoin would rise from its current purchasing power equivalent market cap of 700 billion to 100 trillion (so a 140 fold increase in purchasing power equivalent price) whereas gold would rise from its 12 trillion current market cap to 100 trillion (so an 8 fold increase in price).
