There are several occasions where this would be awesomely useful to the current Spine editor. When you bring in several frames of an animation that you want to all line up, when you bring in a character that you will later whitespace strip, etc. etc.

Please add this if you are able, it'll save me hours of needless work.

One alternative you could implement in the short term if an align tool would take long, is to put multiple images on top of each other in stead of below each other when you drag multiple images into the workspace.