Is IfcProductDefinitionShape a 1:1 relationship?

I would support an official (IFC5) method of simplifying how we reuse geometry, and have 1 way that works for all cases. I don’t want to add another way of doing it in existing schemas, even if it is "nicer’, because in practice that just adds more complexity, as you have to support existing ways and a new way.

As far as “I haven’t yet come across a BIM authoring vendor which has been able to preserve the full fidelity of the shape representation reuse tree.” - that’s a huge philosophical can of worms. There is no current IFC4 MVD that actually even supports that workflow. Almost everything that’s been done to promote preserving parametric information has been over and above what IFC officially supports. Again, I’d rather see extending IFC5 in a meaningful way that supports design transfer for the cases that need design transfer, instead of bespoke solutions.