Well, I remember a year or so back there was a thread about linking audio cues into your health//energy bars.
That would rule, IMO. Perhaps a single 'bip' sound every quarter-bar of energy. Or you could set up a sliding scale sound that would start out high as you jetted and get lower as your energy ran out. Might be annoying if you're using a blaster, though.
Halide's LowAmmo script does something similiar--it'll beep at you when you hit your defined low ammo percentage. I'd definitely like to see that in T:V.
An audio cue for when you get pinged by enemy sensors would be nice as well, and there's a script for that in T2 right now.
Other ideas:
A cue when you first pick up someone on your armor's visual sensors. You come over a hill, say, and you hear a 'ping-ping', telling you that there's two enemies within your line of sight. Not a constant ping, just a single one for a single person, every time they come into your armor's sensor range.
A better skiiing audio cue than T2's. As it is now, you get the 'whssst' sound when you're making a good ski and nothing when you're not. It would be nice if you could toggle it the other way around so that you get your cue when you're screwing up instead.
For vehicles: Definitely need a 'pull up you dumbass, you're about to hit the ground' altitude warning sound.
Flags: Different flag cue sounds for friendly and enemy flags. I know there's packs out there to fix that for T2, but I'd like it to be default for T:V.
C&H: It would be nice if the different objectives on a map would make different sounds when they were capped. Say the center objective goes 'boing', the west one 'pop', the east one 'ping', and so on. Doesn't have to be loud, either. Selectable by map author.
Shields: How about if shields made different tones depending on how much energy they had left when hit? Starts off low, goes to high as the energy drops, for example. Audible to the shielded person and anyone nearby--good for HoFs, as the LD would have a good idea of how badly the heavy is being beat on without having to actually look. Also would be handy for indoor combat against shielded heavies, as you could tell if you were actually hitting him hard enough to punch through.
If you still have the ability to give commands//waypoints to teammates, audio cues for those would be nice as well. T1 had this down pretty well ("Deploy sensor at waypoint!" and so on) and there's a script for T2 that gives you a 'beep' when a command shows up in your chathud. I wouldn't mind the T1 style voice ones, myself.
Not a cue, but T:V needs a whole buttload of voice-binds. Stuff like what I ended up recording for Legends--NME has a HOF, HOF is cleared, stuff like that that never showed up in the T1/T2 voicebind menus.
Perhaps a very, very faint deployable turret hum so that if you listen carefully, you can tell if there's one around the corner? Better yet: if there's more than one, you can hear the way the hums interact and determine number by the resultant pitch or something.
I'm sure there's more stuff that can be done with audio cues, but that's a start, neh?