I would like to see an implementation of llPlaySoundTo, llLoopSoundTo, llTriggerSoundTo, and llLoopSoundMasterTo/llLoopSoundSlaveTo/llPlaySoundSlaveTo that functions exactly like the existing functions, but instead of playing for everyone can be targeted to a single agent.
The only reason I feel this might be a bad idea is that there is potential for abuse here. But I'm pretty confident there's some way we can work on a solution to that. Being able to do this would enable you to do things like play music while a game is in progress in an area that might have 10 games being played. Instead of all 10 players hearing all 10 games playing music (which would be a racket!), they would only hear the sound directed toward them.
While I know there might be other solutions, such as a HUD that uses llPlaySound, I'm ideally looking for something in the code itself that does this without the agent having to wear a HUD.