In case anyone is interested, I have some sample code on GitHub for adding a static, toggable legend to the Shortlist app. The legend is an unordered list. You'll have to create images to represent the items in the legend.
A description of the changes to the app and a demo are located at GitHub - pmacMaps/shortlist-storytelling-template-js: ESRI Shortlist story map application with cust...
Patrick,
Great -- thanks for sharing this with the community!!
We love when developers customize the apps, and we love even more when they share their handiwork so others can use and/or learn from it.
Owen