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This would be a simple plasmoid useful for the panel, or otherwise cluttered desktops.

The plasmoid would be an empty, scalable container you can place other plasmoids in. A button set to either one of the edges, or one of the corners, would shrink the plasmoid to only the button, and an optional label. That button might be interchangeable an arrow, or an icon the user can replace the arrow with.

For example, I have 4 desktops, and the pager on the panel. The pager is eating up my task manager. I place the pager in my "HideMe" plasmoid, along with maybe show-desktop and show-dashboard. I change the arrow to be a more appropriate desktop-icon. Now, when I click on the icon, it will either hide or show the contents of the HideMe plasmoid. If set vertically on a horizontal plasmoid, or vice-versa, it might behave more like a plasmoids-filled-drawer.