Hello Teun,
Because you told me that you not interested in any commercial software I did not answer. But if anyone whants to know if there is software to read IFC to native Creo Elements objects you can see a result of this below.
A model loaded in BimSight.
The same model converted to Creo
Off course it is possible to export Assemblies to IFC object. If you are familiar with BIM you must ask youreself what is the level of detail (LOD) i want to use. In the most common software where you can export a model to IFC there is no possiblity to chance the LOD for the several parts in the assembly.