Will bitcoin ever replace currenries we have today ?
It might happen, but a sort of a revolution has to occur whereby people will lose faith in centralized monetary system i.e if they don't think their money is no longer safe.
maybe an
1/
8th of the worlds population
If the USD, the Euro and the Yen collapse relatively to hard assets, Gold, or Bitcoin people will see the value of a decentralized currency that is not daily manipulated by the State