I feel like IKEA likely operates in a pretty restricted problem space compared to a general knowledge graph like wikidata or what have you. I don't know that you can separate the "all knowledge" graph into 3 layers like this.
(Edit: removed needlessly snarky wording.)
Good on IKEA for solving the problem they have efficiently, but I can be interested in a larger scope.
The 3 layers mentioned are just the basic structure of ontologies. Concepts eg “vehicle, person, desease, atom, bridge,…” then categories of the concepts, and finally data, ie instances.
Larger knowledge graphs don’t grow by adding more “layers” they add more content to all three layers.
I thought that it gets complicated because you can have concepts of concepts, and you can have both categories of concepts and concepts of categories etc etc. It ends up being more than 3 layers, and you get layer violations and loops etc.