For now, only attributes of Dynamic components (library), IFC classifications and advanced attributes are are natively exported ( not correctly, though)
You can edit and add, but it is not coming out. So while they could be usefull inside SketchUp, other software has no direct access to them.
We need clear guidance how to add universal libraries to Objects and how to export them correctly.
Meanwhile, the IFC is constantly developing and SketchUp needs to keep up with them, or it will loose contact with the aec-industry