As suggested by Noémi Balogh from the GRAPHISOFT Community portal, I reopened an old wish for the proper implementation of IfcSpatialZone within Archicad. It was archived due to the lack of what they consider a minimum number of votes to take it into account (>100).
🗳️ Please make your vote there: https://community.graphisoft.com/t5/Wishlist/Publish-IFC-using-IfcSpatialZone-class-instance/idi-p/653086
Fortunately, using Bonsai, you can use this non-hierarchical spatial structure class, and even simulate the suggested specification within the official bSI IfcSpatialZone Technical Report.
Thanks!