Hi, I know this is an old topic (sorry!) but I would like to add myself to this question, since I need also to export a single frame of an artwork to JPEG or GIF when making ads. Many networks require an fallback image they show if they can't show the animation, or while loading at the very start.
For one reason or another, a static image is needed and now I have to screenshot and process every piece (cut the image, change resolution to 72 ppp, save as JPEG). Exporting to JPEG or GIF from a specific frame in the animation would be great for me and sure, other people.