I think its possible but in recent not possible to overcome the central Banks.The reason behind government won't let this thing happen, they won't permit any decentralized framework take over the banks and other than central banks is much imperative since we still require it to cash out our cryptocurrency, imagine if there's now not a bank at that point for beyond any doubt no one can change over their bitcoin or any altcoin into fiaJust think for a moment if BTC overcome so fast how will manage the variable rates and retailers will not accept to early till they well trained and aware about Bitcoin.
We know that no matter how good the system is, if it is not legalized by the government, it will only be in vain, we cannot fight it, so we must obey the government regulations. Therefore, I think that in the near future, the central bank will remain the government's trust for legal transactions.
The government will always go with the central bank so it's quite impossible that bitcoin can kill a central bank because it's not even legalized as a currency by the government itself. And i really don't think that bitcoin will kill a central bank intentionally.
Bitcoin is here not to compete with our fiat in the first place but to serve as an option from the existing currencies we already have. If people prefer to use bitcoin rather than the existing currencies, then maybe its where they feel comfortable and convenient to use it.