Always wanted to build a SaaS around services meant for static sites. Feel free to take these ideas and run with them since I don't believe I'll have the time to follow through with these anymore.
1. A content suggestion tool where based off of the current content and past content you'd build an interest profile so you can populate suggestion widgets on the page, while also not recommending articles they have already read before.
2. A user option to hide read content. When they read content, the link will be hidden from the site so they don't waste time sorting through old content to get to new content. I was planning on pairing this with the option to hide a story that's not of interest for the same reasons. All these articles can be viewed again either by turning off this option(provided the developers integrate it) or by viewing a page with all the content that has been hidden(or however the site developers integrate the api to access hidden content).
3. A favorites/history tool for users on a site. What I had in mind is being able to allow users to favorite content and this will be saved and accessible by the site developers through API to integrate, such as the obvious favorite's page.
Had a few others but don't remember off the top of my head.