I feel like this is something like bringing the oral storytelling tradition to modern media. It allows for change, critique and so forth.
From the site:
Wizard People, Dear Reader is an unauthorized re-envisioning of Harry Potter and the Sorcerer’s Ston, by Brad Neely. To experience it, viewers need to get a copy of the first Harry Potter movie and watch it with the sound off, replacing Neely’s narration with the original soundtrack.