I think that in the future, browsers will gradually gain more use in features other than just web browsing. Browsers already have built-in pdf viewers, and I think it’s only rational to extend that functionality to Markdown and EPUB files. There are extensions that do this, but it’s clunky and requires more steps than necessary.
Adding markdown and epub viewing support would make Brave unique in the browsers space, and fill a niche that contains more people than you might think. Because of the nature of Markdown(and latex rendering), implementation would be fairly straightforward. In addition, because of EPUB’s popularity, you’d be hard pressed to have difficulty implementing book viewing.
Brave’s PDF viewer, while linked to chromium, is still fast and simple, which is all most people want or need. I think having something similar for these other formats would be distinguishing and beneficial for brave’s future.