Traditional Software Engineering (SE) courses often prioritize methodologies and concepts in small, controlled environments: naive projects used as a proof of concept instead of full-fledged real software systems. Although this strategy has clear benefits, it does not place enough care in training students to face complex, non-trivial legacy software projects. To bridge this gap, novel SE courses are leveraging the rich variety of open-source software (OSS) projects to illustrate how these methodologies and concepts are applied to existing, non-trivial software systems. To better understand the benefits, challenges, and opportunities of this transition, in this paper, we interview seven SE professors that changed their academic setting to aspire students to comprehend, maintain, and evolve OSS systems as part of their SE course. We found that there are different ways to make use of OSS projects in SE courses in terms of project choice, assessment, and learning goals. Moreover, we evidence clear benefits of this approach, including improving students' social and technical skills, and helping students enhancing their resume. Also, we observed that this strategy comes with costs: the activity demands effort and time from the professor and the barrier for one getting involved with and, therefore, placing a meaningful contribution, in an OSS community is often high.