Seems like it should be a relatively simple fix. I was annoyed by this twice in the last week. I'm sure you've all been there... watching "episode 2" only to quickly realize (or not so quickly if you've recently returned from the pub) that you've already watched it.
This was a great idea. I’m guessing because plex logs the episode twice into the database with the same media file, so you’d have to have relational data to bind them and mark them watched. Or, they’d have to run another query to the media location table, then loop update queries to mark the media in the metadata table.
I’d have to look through the mark un/watched code and really examine the database to see how they have it setup now. But this is completely doable and would only affect the single episode un/watched query. I’d say it’d take a dev who was already familiar with the code and database structure 10-15 mins to do. An hour tops.
I would definitely like this feature. I have tons of podcasts and find it difficult to track what shows I have already listened to if going back into the archives.