Erwin, are you talking about a folder structure in a custom library in order to add surfaces one by one, or are you suggesting that you are able to have a folder structure in the surfaces list when you go to choose one for an object.
If that's confusing, I'll elaborate:
Option 1:
To add a surface you go through a folder structure in your library and choose the surface to add
Option 2:
I create a wall and want to change the surface. When I look at the list of surfaces, I have a folder structure that organizes everything
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