Thank you for your honestly and your willingness to share. This heartfelt.
A few ideas:
Make it a platform. Others might want to use the app to create their own stories. Would they pay for that ability? Something to be tested.
Offer a service to authors. Take their book, and make it into a hardbound story. They pay for the cost of creating that as a marketing expense, and it builds the hardbound content.
Take the hardbound stories and turn them into YouTube videos. Add a voice over, you already have some of the animation. This could extend your reach and find new readers.
Offer a service making hardbound stories of the history of a company. Would Facebook pay for their company history in hardbound format? Perhaps.
Regardless of what you chose, I think highly of the product, and more importantly you.