Without central banks, bitcoins won't exist. They are both in a different class of their own. None have to replace the other. Why should they? Irrespective of what we thing of the government and global financial institutions. I don't mean to sound pessimistic but if bitcoin "kills" central banks the world would experience chaos like never before besides I believe this was never the intention by Satoshi when he/they created bitcoin. We really have to chill and stop sounding like the group on Reddit Forum that want to see bitcoin die.
Bitcoin is currently present as an alternative currency, especially the digital currency. In terms of function, Bitcoin is considered to only be able to fulfill some of the functions of currency, namely the means of payment, commodities whose value is a general consensus of the results of the acceptance and trust of the public. Like gold, diamonds, banknotes, stocks in general. And Bitcoin has expensive values because there are real money stored by Exchange which is backups from Bitcoin prices. The Bank Cryptocurrency (Dex) model serves as an alternative. Bitcoin/Alt is the money.