The problem with this is the question of who will be the leading country who will launch the centralized currencies? What will be the basis to be qualified? Who will be the authorized persons to do this? But beyond those questions, the fact that clear rules must be set prior to that.  I guess, if we have centralized currency, the authority can manipulate the flow of money easily.  They can also control the production of money as well as its value.  More people will be having the idea of counterfeiting the money since there will be only one pattern of money.