Would be very useful highlight the components that can accept a given component during the drag and drop action.
Imagine you first put a Camel Route in your new/empty diagram. Then you start designing your route. Some containers can accept only specific components inside it. Eg: a Choice need at least one When and one Otherwise. So during drag and drop, when you pass over the right container (the Choice in my example) it should be highlighted (with a colour) indicating you can pull that (when or otherwise) component there.
it make sense?