I would love to see the addition of a double-ended arrow in the Image Editor.
I envision selecting it by right-clicking on the existing arrow button and then having the option to pick either the single- or double-arrow type. It would function exactly like the existing single arrow, but with an arrowhead at each end.
I use this often for showing dimensions between two lines by stacking two opposite facing arrows. It would be great to simplify that to a single drag-and-release action.
Windows 10 Pro Version 1809 on a Thinkpad P51