Absolutely, sometimes you want to be engrossed by the film. I imagine it could be useful for a lot of video content, that's a great use case you thought up right there. 

Also.
Adding more info to instructional videos? 

# KARAOKE 
Nostr Karaoke 

 Streams could use it to sync the chat with the playback on later viewing.

subtitles for every video could be crowd sourced/AI generated, a nice accessibility feature