In ArcGIS Pro 1.3.1, I have just looked for the ability to start legend items in a new column.
This functionality is present in ArcMap's Legend Properties on the Items tab which appears below:
Has anyone found the equivalent functionality in ArcGIS Pro, or know when it may be expected to appear?
It is not mentioned in the Work with a legend documentation.
Nor does it appear on the Element: Legend Item
pane (see below)