Scrolling down after the article could load articles in the same category as the current article. This would work well for geographical articles, if I get a page about a water canal in Germany and I decide I want to read about every single canal in Germany (or every type of skin disease or every type of sorting algorithm or every type of butterfly, etc.), I would keep scrolling down instead of left, then after that category is exhausted it would start showing some broader category, i.e. canals in Europe and then the world and then waterways.

One way to choose which category to use would be looking at all the articles in all the categories of the current article and finding the category that has the most repeated articles (for example if a page belongs to 5 categories, use the category that has the most articles that also belong to all 5 categories), essentially the most specific one and then keep getting more generic. A second pass would be learn to throw out overly specific, uninteresting categories like "Canals opened in 1922". A third feature would be to magically figure out which category I'm interested in. Another feature would be to show the category I'm currently scrolling and what fraction of the articles in it I've read, this would also be a good place to make it a clickable drop-down that lets me choose to follow a different category, but that's antithetical to the TikTok idea.

P.S. love the name but TikTok's lawyers will probably tell you to change it if this gets any traction.