One potential solution would be to create a new type of geometry representation that is merely a proxy URI to an external library. That external library can then handle the rest of the geometric, rendering, compositing, material, texturing, etc details, in a similar way that document reference URIs work. This is essentially a similar proposal to IfcExternallyDefinedSurfaceStyle, except that it is for the shape representation.
A related issue is that I believe the current set of IfcSurfaceStyleLighting needs a few extensions to allow archviz to do their work. I would expect a property for RMS facet slope of the surface, or “roughness” in short. I would also expect whether the material is metallic or nonmetallic to be defined as an enum, as that greatly changes the rendering simulation results. This should cover the majority of basic cases I believe. The rest can be covered by IfcExternallyDefinedSurfaceStyle.
But of course, geometry and materials only make up a small aspect of archviz. Is the BIM model to include metadata about marketing shots? Or view corridors that the architect promised them they would see? Or if there are privacy requirements in the BIM model? Or line-of-sight requirements? This opens up the debate about storing IfcProject associated camera angles, etc? Maybe too much to chew on right now.