Bitcoin nowaday is a currency but tomorrow who know? People are trading on the exchanges everyday, using bitcoin as main currency. So, we will have a different COIN to change Bitcoin but not now, it's in future.
if bitcoin becomes the main currency it is impossible because the state and the government more trust with the original currency of the country's bank. bitcoin no one controls and can be used by everyone / anonymous. fear later if bitcoin is used as the main currency, bitcoin will be used as a crime that will harm the country. there must be a control and set the bitcoin first so that bitcoin can be a currency.