I would love to see Plex show a list of related movies regardless of them being in your library or not.
Where I think this really comes into play is for movies that are in a series.
I have most of the fast and furious series. I would like to know what order to watch them in because they don't use a numbering scheme to their movie titles. I would like to be able to select one of the movies and be able to see that it is part of a series and see the list of all the movies in the series. This would allow me to see that I am watching them in the right order.
This also helps with other movies that are a follow on. For instance, I recently watched Riddick, only to realize part way through that there must have been a pre-cursor to it. There was - Chronicles of Riddick. I started watching that to realize that there was a pre-cursor to that as well - Pitch Black. Wouldn't it have been great if Plex would have told me when I was on Riddick that there were two movies I should watch first.
Then wouldn't it be great if I could watch a trailer of each of the related movies. Here is a great use case for that. My wife and I were about to sit down and watch RED 2. We knew that RED came first and that we had watched it. But we didn't have RED so I couldn't go to RED in Plex and watch the trailer for it. But we wanted to watch the trailer for RED to remind us of what happened in RED before we watched RED 2. I had to break out the laptop and pull up IMDB to get some trailers.
Thanks
Greg