Unfortunately, if an organization needs to be decentralized, it means it is already somewhat centralized. Decentralization has to be done from the center that exists, except in the case of revolution.

What can be done to decentralize? Reverse one of John XXIII's policies, and go back to putting priests and laypeople in charge of the Curia. There is no reason for a bishop to run a pontifical council, unless you want to centralize power. Have selected bishops gather to elect a new pope, rather than leave it in the hands of the Curia. This could never have been done before because of the travel times from Africa to Rome, but airplanes mean a bishop from Australia or any other corner of the world could arrive in time.