When we share MapStories on social networks they tend to be a single screenshot. We should investigate animated gif and video outputs for MapStory, as that can make social sharing communicate the motion inherent in the stories.
GeoServer has an animated gif output already. One limitation is that it won't work with base layers like google or openstreetmap. But if we host our own tiles then it should be possible with cascading the WMS from those. Will need a UI to let people create it.
Another option is video. Quicktime may be a good option, or a more open format. Ideally would be same UI as the animated gif, but would have less limitations on size/frames.
To work with twitter cards we'd need H.264 format. See https://dev.twitter.com/docs/cards/types/player-card