There’s actually a feature suggestion to allow some kind of fingerprint / soundprint / … media recognition. The key challenge with that is there’s no reference for those. Some argue that Plex is in a particular good position to use their existing matches to establish such a reference… I can only guess this could be a thing in the future. Compared to audio/music recognition there’s just a whole load of additional complexity (i.e. different translations, cuts…) that need to be covered; so while you can recognize a music track based on a few seconds and a handful of media characteristics, doing the same for a movie will need significantly more power – and I’m not sure users will appreciate if Plex starts scanning/processing Terabytes of their data to get an accurate match.
