Another angle: the user might have found a similar service that requires login or subscription, and they want to develop an open or freemium version. So the feature should be scalable and secure, allowing for future monetization if needed.
Storage options: Storing the actual media files could be done using cloud storage like AWS S3 or Google Cloud Storage for scalability. The frontend would request the file from the backend, which then streams it from the cloud storage.
Testing: Need to test the download speed, especially for large files, and ensure that the server can handle multiple simultaneous download requests without throttling. Load testing tools like JMeter could be useful here.
Compliance: Even if fictional, it's good practice to consider privacy laws like GDPR if dealing with EU users, just in case.
Notifications and Feedback: Informing users when the download is ready or if there's an error. Maybe sending a download link to their email after a successful purchase.