The 6G mobile communication system is facing a dynamic and complex network environment, with diverse scenarios and personalized demands that pose significant challenges to the provision of network services and value realization. Therefore, 6G networks should transition to a new paradigm that is “service-centric", integrating advanced network technologies and multi-dimensional network resources to achieve on-demand services across all domains and scenarios. This article provides an overview of research on 6G on-demand services across all scenarios. Firstly, it highlights the necessity of on-demand services and outlines the research value of on-demand services in all scenarios. It proceeds to expound on the essence, challenges, and foundations of on-demand services in all scenarios. Subsequently, it analyzes the architecture and key technologies for 6G on-demand services in all scenarios. Finally, the paper offers a prospective outlook on the future and potential research directions for 6G on-demand services in all scenarios.