It is Clear that bitcoin will be the only Currency for payments
What is the evidence to this, we cannot conclude yet, bitcoin can be the mainstream digital currency but doesn't equally means that the world will only have it as a means of payment, fiat may also exist along and the future ahead will determine which one will the people value more with higher priority.
Like there will be no Cash or VISA
we can't say as well, not until we see what comes in with bitcoin global adoption and the way it has been accepted as a legal tender by many countries, but we are definitely heading somewhere.