I have been working on a sketchfab exporter for FreeCAD:
The discussion thread on the sketchfab forum is here: https://forum.sketchfab.com/t/freecad-exporter/12903/2
and the branch: https://github.com/yorikvanhavre/FreeCAD/tree/sketchfab
There are still small glitches to solve but it is working already.
The idea would be to add this to the web workbench, it's a rather small script. Only it would *kind of* show inside FreeCAD a commercial product. I know that the most radicals here will probably complain, but the sketchbab people are cool, many of them are from the Blender community, and many other open-source apps (Blender for example) also have a built-in sketchfab exporter. Although sketchfab is not really an opensource thing, I think it is very opensource-friendly, so I don't see why not.