A world model itself, in its particulars, isn't as important as the tacit understanding that the "world model" is necessarily incomplete and subordinate to the world itself, that there are sensory inputs from the world that would indicate you should adjust your world model, and the capacity and commitment to adjust that model in a way that maintains a level of coherence. With those things you don't need a complex model, you could start with a very simple but flexible model that would be adjusted over time by the system.

But I don't think we have a hint of a proposal for how to incorporate even the first part of that into our current systems.

Sounds like the “open-world assumption” used in RDF, with coherence maintained by OWL. (Well, at least it’s a hint of a proposal.)