Hi @mangelozzi
kicad devs are working for a direct integration of STEP using the same approach I did with FreeCAD:
converting STEP to VRML and display natively the STEP->VRML model in kicad…
This part is almost done using OCE, which is the main MCAD library engine of FreeCAD…
Then there will be the part to export pcb board and models to STEP… this will take longer I think…
my kicad StepUp tools are available now and they probably will cover the STEP exporting process until a full integration will be done…
kicad StepUp is covering:
- kicad_pcb to STEP exporting
- kicad_mod visual align 3D model over footprint
- generation of STEP model for pcb and parts configuring ‘bounding boxes’ and ‘minimum volume’ of 3D parts
- collisions detect for enclosure and footprint design
- exporting of VRML models with Material Properties (almost public feature)
Many of these features will remain in FreeCAD (MCAD) environment anyway…
Moreover the direction is the same: leaving VRML files coming from Wings3D or similar modeler and get only STEP 3D mechanical models library as the source for kicad 3D 
That is the reason I’m calling for an official repository for 3D mechanical models
The StepUp made by @maui is a tool GUI and script developed for kicad ECAD MCAD collaboration and to be used with FreeCAD 