The ability to see a preview of the canvas in the selected aspect ratio before publishing in the Animation workspace.
See my post here for all the details: https://forums.autodesk.com/t5/design-validate-document/how-can-i-preview-canvas-aspect-ratio-for-pu...
Meta note to Autodesk: Please give us the ability to copy the HTML from our own questions so that we can migrate them to IdeaStation upon request by others.