You should enable the users to save downloaded subtitles into the file location (including files located in remote servers).
I’ll explain why I think this should be added to the app. Some time ago I was streaming on my iPhone a movie located in my NAS and with subtitles downloaded from the Infuse App. Since I was unable to see the entire movie, I tried to finish it after in another device (my TV) but I had to turn on my computer to download the subtitles again… I went to all this work because the movie deserved to be watched in a big screen (not in a iPhone 5 screen).
Hope to ear from you soon.