The biggest change I want to subtitles is to be able to turn them OFF and keep them off globally. I have a lot of TV episodes with subtitles and it's really annoying to have to be playing a whole season and have to stop each one when it starts, find it, turn off the subtitles and restart it.
Yes, I also searched for that option.
That is indeed a problem when you´re watching a lot of content in sequence, because some people (like me) never really need subtitles, apart from rare cases where there would be an interview or such in a different language, which is subtitled. Then I would want to turn them ON, but in like 99,9% of all cases, I want them to be OFF.
The current behaviour probably has something to do with both how Air Video HD works internally, because it is a kind of "store the settings per file" approach (which is great for some content, but is annoying if there are movies that are split over several containers (Blu-Rays) or TV episodes you watch one after another as a single file) and because a global option for turning them off could interfere with the way some content (like DVDs, etc.) are meant to be viewed. Air Video HD would basically overwrite everything then, because you told it to turn it off globally. It still should be implemented, though, because it is a helpful (and time saving) addition.