Assembly-oriented software architecture is transforming how modern systems are developed—shifting focus from writing code to composing business-aligned capabilities. While modular components are increasingly common, most remain confined within organizational boundaries, limiting their reuse potential. This paper envisions a capability marketplace that enables cross-organizational sharing, discovery, and composition of semantically rich, contract-governed, and deployable software modules. Unlike traditional code repositories, this marketplace promotes scalable reuse of high-level capabilities supported by trust modeling, interface verification, and lifecycle governance. We outline the conceptual architecture and key design mechanisms, and identify open challenges in trust establishment and developer workflow integration. By rethinking software engineering as ecosystem-scale composition, this vision aims to advance a more composable, collaborative, and sustainable model of modular development.