Here's what I'd like to be able to do.
You have a rectangle with no fill but inside this rectangle you have two others. The key is that the outer rectangle is in front of all others. If you grab the regular eyedropper tool that's on the main toolbar you can "pluck" the color from any shape but you cannot fill any shape that's within the outer "front" rectangle. Would be nice if I could grab the one I want to change and either have an option to "fill from other shape" whereby invoking the arrow to let me choose the other shape OR hit a macro shortcut to invoke the other eyedropper tool in the image above.
I know it's not what you're asking for - but what about the right-click-then-drag-and-drop-using-Shift way of copying a fill from one shape to another?
Eyedropper to fill fails to "dig" to shape
I don't do that often enough to have the use of Shift for that as "muscle memory". I am more likely to do the right-click-then-drag-and-drop thing, and then use the menu that pops up to choose what I want to do.