It is possible if the government of ones country will accept cryptocurrency as a decentralized system  but i think it will not totally eliminate the banking system also to cater individuals that will prefer not to engage in cryptocurrency.  For those banks who wanted to cater cryptocurrency is also ideal as to cater the need of individuals who are engage in cryptocurrency for businesses, trading and investment. Maybe it could be a link only.  Although they are plenty of advantages over banks but still we cant predict how it works in the real world of banking institutions,