You talked about Properties editor tabs because of icons shown in buttons.
But exactly same icons are used in Add menu (shift A) that permits to add objects to scene.
They are used in outliner too, to represent objects. In 2.79, they are shown in Create tab of toolshelf.
I just understood the use of these icons in a toolshelf as a quick access to objects creation.
In 2.79, Shift Ctrl C is a menu to add constraint. If you pass through search to launch Add Modifier operator, you will end up with same kind of menu. You can add a shortcut to this operator.
In 2.8, it looks like a modifiers sub-menu is missing under object menu to be able to add it to favorites menu.
So, after that 2 examples, we can understand that last 2 icons could be to add particles and physics effects.
In video dedicated to grid layout, pablo says that user may have control of width of column through python.
You can zoom in and zoom out in a properties editor.
I don’t know if width of column could take that into account ; or , if it is preferable to let user adjust zoom and width independently to allow him to have abbreviated labels but bigger values.
IMO, a column width should be a value inside header of properties editor to have it adjustable per editor. But it will probably not fit into a vertical header.
It could be a popover. Click on icon on header → popover containing a slider → Use slider to change aspect of interior of editor.
I would prefer a multiple columns like in d.b.o. task to a grid layout. So, maybe a popover for properties editor could contain a preference about that. Maybe, it could also contain other preferences like text alignment or decorator/panel hiding.