The problem with that is scale.
Plex doesn’t store information about which items in your watchlist are on private Plex servers. The check if an item is available on a Plex server is done locally in your browser for each item. More detailed explaination in my other post here.
This is okay for the individual media page since it only checks one item at a time and only when you click on it. For Plex to display items available on a private Plex server from the entire watchlist could potentially be hundreds of API calls. That is just not scalable and Plex does not want to save/cache the list of items on your server due to privacy.
Example:
- I have 10 items in my watchlist.
- I have 2 personal Plex servers.
- I have 8 Plex servers shared with me from friends.
- 10 items * (2 + 8) servers = 100 API calls to check if any items in my watchlist are available on any Plex server.
- Scale that up to 100 items in my watchlist and that is 1000 API calls.
