As title says, I am looking for an extension that allows the user to delete all materials (faces, groups, components) from the selected geometry, basically returning it to default. Exactly as it would be if you deleted all materials from the file.
This can be done natively now to all the objects at the same level by clicking the material swatch in the Entity Info panel. Then choose the default swatch from the popup.
Are you thinking that you want this to “dig down” and removed all materials from the child objects in nested levels ?
If so, doing this will affect all instances of groups and components even those not selected.
Yup, same as it would when you delete all materials from a file.
I am trying to bypass having to cut selected geomtry, paste it to new file, delete materials there, copy again my geometry and paste it back with no materials.
SketchPlus has several Unpaint tools that do what you want