This idea has been merged into another idea. To comment or vote on this idea, please visit WEBFLOW-I-4063 Ability to set aspect ratio of images (e.g. 16:9) in the Designer.
Have new units W and H which reference that classes values set for Width and Height. This would make it easy to create elements with a certain aspect ratio. Say you had a DIV that you wanted to always be at a 2:1 aspect ratio you could either set its width to '2H' or its height to '0.5W'.