I always thought something similar would be a cool side project. Annotating plot, character overlays, subtitles with the name of the character for easier understanding, etc. Prime Video has some feature that lets you see the characters in each scene. Getting at least some annotations done by hand would probably be not too difficult - some shows and movies have some VERY dedicated fans.

I've attempted to start with something basic - some code to pare down an audio stream into basic hash identifiers a la Shazam - so that media can be identified regardless of quality etc (even encoded to 64kbps mp3, for example). Which is surprisingly difficult...