Since the 2.0.2018.x version, you can add or remove columns in an article layout by dragging the right or left middle handle. Since the 2.1.2440 this functionality is enabled only if you select the personal preference.

Select the entire article layout and hold the CTRL key while dragging the vertical middle handle in the desired direction.

On the following screenshot, the top layout is the original one.

The layout in the middle is obtained by dragging the right middle handle to the right, while holding the CTRL key pressed.

The bottom layout is obtained by dragging the left middle handle to the left, while holding the CTRL key pressed.

 

Technical note

This change is in the Public Overridable Sub OnAction in the PageDesignerAddIn class of the Page.vb, in the code block starting with:

If r.Width <> Page.GetSelectionWidth And Fred.GetQualifier = 2 Then