How cool would it be to be able to play sound effects or background music in a storygame? I'm not exactly sure how it would work. My guess would be uploading mp3 files to the site and then selecting them from a list. Another idea would be copying the code to a link and embedding it from a source that's already online.
As far as functionality goes, the storygame creator can choose how many pages the song can go on for, which pages to not play anything for, etc. If the sound is a voice-over (for a character that talks) you can also do the same thing.
This is probably going on a stretch, but I think it would be pretty awesome.