A powerful set of educational tools has emerged over the last decade with the rise in the adoption of online adaptive learning content. An increasingly popular tool in this space is the "intelligent textbook" as a platform to support and distribute content for e-learning, given its resemblance with real-life physical books. Existing efforts in this direction include the development of digital textbooks where both textual content and interactive learning activities (i.e., examples, problems, etc.) are carefully handcrafted by the authors so that they are perfectly placed to follow the knowledge acquisition-practice flow. However, this approach is very time-consuming, and it requires the work of high-expertise authors. In this work, we suggest and discuss a more scalable solution: we take existing digital textbooks and augment them by using repositories of existing online learning material associated with the subject matter. We present our current work in this direction and discuss challenges and opportunities for future work.