It look like this is a very old discussion and I think this might be an old solution but I think I've found a way to get stacks and particles to work in Theatre View with some custom filters.
Has this been done before?
I setup another filter view under Movie called Movie Extras and then added Series and a Season filter to that.
Then as a test I tagged each particle with a different Season with a short description, eg: 1 Movie, 2 Trailers, 3 Extras, etc etc
I tagged the Series with the movie name.
I tagged each particle as episode 1. Not sure I needed this, but anyway.
Now I can collapse the particles stacks so only the movie shows up in the normal theatre view, and If I want to see the extras, I go to the Movie Extras roller and find the movie, select it and drill down into the movie and I can see all the particles with their individual descriptions so I can pick what I want to watch from the extras.
I'll post some screenshots tomorrow when I've had a chance to tag a few properly and you can tell me what you think.
I'm guessing you could also group tag some of them into Seasons (for example Deleted Scenes as a Season) and have another level below that with episodes for each deleted scene.
And to take it another step further, you could create your own custom database fields for Movie Extras, Deleted Scenes, Extras etc and filter on those instead of using the default fields for episodic shows.