This seems interesting! But as far as I know this feature is not available in ThingWorx Core.
Here are my inputs:
Windows has option to show slide show of pictures as Screensaver. So, we can use one of the ThingWorx Repository folder as input for it.
Save the Mashup as an image (https://marketplace.thingworx.com/Items/PDF-Extension saves export of Mashup in a PDF. You can try to create an extension which saves it as image).
Else you will have to create your own custom Extension for this feature.