Software supply chains (SSCs) are complex systems composed of dynamic, heterogeneous technical and social components which collectively achieve the production and maintenance of software artefacts. Attacks on SSCs are increasing, yet pervasive vulnerability analysis is challenging due to their complexity. Therefore, threat detection must be targeted, to account for the large and dynamic structure, and adaptive, to account for its change and diversity. While current work focuses on technical approaches for monitoring supply chain dependencies and establishing component controls, approaches which inform threat detection through understanding the socio-technical dynamics are lacking. We outline a position and research vision to develop and investigate the use of socio-technical models to support adaptive threat detection of SSCs. We motivate this approach through an analysis of the XZ Utils attack whereby malicious actors undermined the maintainers' trust via the project's GitHub and mailing lists. We highlight that monitoring technical and social data can identify trends which indicate suspicious behaviour to then inform targeted and intensive vulnerability assessment. We identify challenges and research directions to achieve this vision considering techniques for developer and software analysis, decentralised adaptation and the need for a test bed for software supply chain security research.