I wish I had the ability to select a line and change just the thickness of the line (just like you can color). I often draw things and realize the object it too big or small. When I change the size of what I drew, it changes the thickness as well. I'll often misjudge how something looks and not realize the lines are all too narrow or too thick. This would allow me to select them and change them to a new thickness (much like you can color) without changing the size of the object.

Several years ago, there were a ton of folks that were looking for this option.