I think it should be centralised.Their are many countries which are not accepting bitcoin only because it is not centralised.Due to ban on bitcoin in their countries,investors are not investing in it and this directly lower the price of BTC.Moreover crime will be decreased if it will get centralized.But converting decentralised currency into centralised one is very tough.
For now, cryptocurrency is decentralized with all the benefits enjoyed by bitcoin users. However, many countries reject bitcoin because the state wants centralization with the aim of monitoring bitcoin users and bitcoin price movements, where the state has an interest in taxes and protects against criminal acts.