FreeCAD and OpenSCAD do not share compatible data structures, so the data must be formatted twice.
The Model Source Design Categories, Hybrid Models, Special Design Techniques are showing the importance to keep good data, and make it easy to find.
Instead of finding one solution to all models and assemblies, the best way is probably to take each model and create the optimal structure.
What's more, a good design should have the capacity to also generate the 2D assembly drawing - which means the part of the design in OpenSCAD should have the data in a format that is ready to be imported in FreeCAD, to be used by the Draft tool.
This is the place to discuss CAD data in details.