Architectural heritage is increasingly documented and managed through point clouds, photogrammetry, Heritage Building Information Modelling (HBIM), Geographic information system (GIS), machine learning, and immersive media. Yet these technologies often remain fragmented, with weak continuity of identity, semantics, and spatial alignment across representations. This paper argues that heritage digitization should be reframed as a 3D smart-data integration problem rather than a sequence of isolated 3D representations. Building on recent analyses of digital heritage technologies and their multi-stage application trajectory, we propose the Architectural Heritage Information Infrastructure (AHII) as a standards-oriented framework that links Smart Point Clouds (SPC), IFC, and 3D Gaussian Splatting (3DGS) through persistent identifiers, a shared spatial reference, explicit crosswalks, and controlled vocabularies. In this architecture, SPC acts as the evidence layer and semantic proposal space, Heritage Building Information Modelling / Industry Foundation Classes (HBIM/IFC) provides authoritative object semantics and structured attributes, and 3DGS supports lightweight, queryable photorealistic visualization for expert review and public interaction. Two Dutch pilot cases illustrate how the framework can support cross-representation interoperability, semantic propagation, and audience-specific delivery while preserving traceability. The paper contributes a concise conceptual and operational model for smart heritage data, positions architectural heritage within broader information infrastructures, and outlines how building-scale heritage assets can become interoperable components of future smart-city information ecosystems.