I'll try my luck with a feature request that I thing it will be useful for everyone.
I think it would be very nice if Plex could notify you (when you open any player) if a new episode from your TV Shows in your library has been aired.
Let's say that you have some shows that are still in production (Big Bang Theory, Walking Dead) and you have all the episodes until last week. When you open the player, you get a notification that new episode/s from X TV Shows are aired and not yet in your library. Or better, when you open that TV Show.
That can be expanded also to music library. If you have full albums from an artist, when a new album by that artist is released, you get a notification.
I could see something similar with films but it might be a bit complicated. If you have a low-res film that was not yet released on Blue-ray in your library, when the blue-ray becomes available... you guessed - you get a notification. This could be more useful if you had a way to see a list of films that are now in cinema or will be released in the current year and you can add some of them to a notification list and you'll get a message when the blue-ray is available.
The most important part is the one with the TV Shows.
It can only be available to Plex Pass members, I don't mind. I think more social integration in Plex can be a real up-sale for Plex Pass.
Hope someone from the staff will find this useful.