I'd like to be able to clone an existing mockup diagram, so that I can quickly do A/B variations of an idea.
Thank you for the idea. There are a couple options to make this easier. First, you can duplicate a tab in a mockup by right clicking the tab at the bottom of the mockup. The additional tabs will not show up in the preview but they will be available to view by clicking Edit mockup. If you do want to include both variations in previews, we would suggest Control+A and then copy and paste the details into a new mockup.
At this time we do not have plans on our roadmap to address this but we will continue to monitor customer feedback.