A big NO-NO! Crypto currencies were meant to be decentralized. What do you think is going to happen when there is a "central" bank. You think it will still remain decentralized? You think we will still retain our financial freedom? You really think the government won't be using it for their own advantage and to dominate its people? Tons of more questions to ask. Just try answering them and you will understand why it is the worst idea to introduce central banking system for crypto currencies.
That's true, we don't need a central bank for cryptocurrency, this is not going to happen even government will take over in this market because for sure no one will invest. This market is created and meant to be decentralized, its ok to have some regulations but never to control by any government. Crypto central bank is just a dream for every government, we should not support it.