A typical user interacts with many digital services nowadays, providing these services with their data. As of now, the management of privacy preferences is service-centric: Users must manage their privacy preferences according to the rules of each service provider, meaning that every provider offers its unique mechanisms for users to control their privacy settings. However, managing privacy preferences holistically (i.e., across multiple digital services) is just impractical. In this vision paper, we propose a paradigm shift towards an enriched user-centric approach for cross-service privacy preferences management: the realization of a decentralized data privacy protocol.