Early guidance is required to match Industry 4.0 ambitions with an understanding of the evolving Industrial Internet of Things (IIoT) system and its capabilities. Considering IIoT systems and operational methodologies within steel manufacturing, a three-stage evolving IIoT system is proposed. IIoT requirements for selected Industry 4.0 applications are presented and generalized guidance matches the application with the relative support level of each evolutionary stage. The guidance specifically considers digital twins, cyber-physical systems, horizontal and vertical integration, integrated worker health and safety, increased workforce mobility, and advanced maintenance. To demonstrate how the evolving IIoT system aids or potentially prevents Industry 4.0 applications, the feasibility of advanced maintenance strategies within steel manufacturing are presented, including predictive and self-maintenance.