Actually, I was thinking of making it an option in the object editor. When seting up a ship, there would be a field for selecting the default persona for that ship. Obviously, not every ship in the game will require a persona, enemy for example. Ships that are in the mission but are not required to send any messages, would have this field left blank. If we could force the game engine to follow these user-defined defaults, then perhaps when you get a build-in message like those good-shot messages from your wingmen, or "get this bandit off me!", then the heads would match up to the assigned persona. It might however, get hard if you assign a female head, but hear a male built-in message... unless there is already a link between head gender and message voice for the built-in messages.
On a side note, if someone did a complete overhaul and upgrade of FRED, it might be cool to have a small window so you can see in FRED, which head ani you've selected. You'd need to either extract a single frame from the ani for display, or include ani playability into FRED, which could be an advantage if you wanted to see just how long the ani was, to match it to your message length.
Later!