Integrated solutions across processes, sectors, and systems can deliver value that exceeds the sum of their parts. Sector coupling, for example, is increasingly recognized as a key enabler for balancing intermittent renewable electricity, while creating new interdependencies and systemic risks. Yet, the capacity of energy system models to anticipate such synergies and trade-offs remains uneven. This article presents a structured review of Austria's energy system modelling landscape, mapping over 800 publications from 54 research groups. We classify modelling capacities across technical, temporal, and spatial integration dimensions and identify significant gaps in areas such as bioenergy, circularity, and extreme event modelling, alongside promising advances in heating networks, electricity sector coupling, and energy communities. The growing attention to operational flexibility in long-term models offers a window of opportunity to better anticipate shocks, structural breaks, and resilience considerations. The openly shared integration fitness tables derived from this review aim to foster collaboration and capacity-building across modelling silos. We argue that advancing System Integration Impact Assessment requires uncertainty-aware modelling frameworks capable of capturing synergies, trade-offs, and systemic risks. Embracing uncertainty rather than reducing it can help design transformation pathways that are not only sustainable but also robust and flexible. Ultimately, this shift could bring together environmental and economic efficiency, safety, and security into a shared paradigm, elevating sustainable development toward reliable development.