Just a thought...
I see you can attach images to messages in a Message Action in the Event editor. Is it possible to attach other files? A sound file, for example?
If not, perhaps it is something that could be added to the Message editor someday. I can see, for example, adding the national anthem of a particular country to a message telling the player that this country has successfully completed a mission. So, again as an example, if a scenario has the player controlling the Japanese side, the Japanese national anthem plays if you win the scenario.
I'm sure people can come up with a lot of other ideas for sound files, etc.
(I notice you can add a link...I'm not sure if that would work for playing sounds, though.)
Anyway, just a thought.