@keet the concept which YGYL is trying to describe is the same of grouped furniture. SH3D is already capable of handlig this, but lacks the ability to copy this group in the catalog for future use.
Of course you can export the group as a single object and import it in the catalog, but this will be no longer editable and will take more space, since all vertex coordinates have been copied in the new model.
Furniture groups instead don't take up space, because they are just a list of references to existing models along with spatial information about where they should be placed in the plan.
Even in the case where this new kind of object would camepackaged in a furniture library along with vertex data, there is a chance to save space. Think about a group made by a table with 6 chairs: you could have vertex data for the table alone and for a single chair, then the group will say to duplicate the chair model around the table, but this happens at runtime, so only one chair model is actually taking space on the disk.