The pervasive digitalization of our world has ushered in a new era marked by increased complexity and diversity in the development, optimization, and maintenance of modern software-intensive systems. These systems, often characterized by intricate socio-technical components and AI integration, pose challenges for conventional systems engineering approaches and require an alliance of different disciplines. In this vision paper, we argue that they demand a paradigm shift towards integrative modeling across systems engineering, software engineering, data science, and simulation engineering. We highlight the key challenges faced in the development of modern complex systems that need to be addressed by this paradigm shift. We argue that achieving this shift requires new research, tools, and education.