Currently most player sounds are somewhat abstract and are intended to not sound too masculine or feminine like was the case with the pre-1.0 hurt sound. I think a mod that allows for the player to choose the way they sound, and add more human sounds to them, would be great for immersion and character customization.
- Voice types: you could have no voice (the current vanilla behaviour), man, woman, boy, girl, maybe some gender neutral options
- Breathing: there's an existing unused sound for this, but it might be interesting to have a quiet breathing sound for when idle, and perhaps more intense panting when sprinting. Snoring/yawning while in a bed could also be added, and more shaky breathing could happen in cold biomes
- Hurt sounds: we could have minor dismissive grunts for insignificant damage to more intense shouting in pain for more serious injuries (think like how it works in Happy Wheels). More specific sounds for certain types of damage such as drowning could also exist
- Using items: for example, when throwing something, the player could emit a sort of ugh sound like you would when putting effort into it - could also apply when using melee weapons
- Eating: the existing eating/drinking/burp sounds could be replaced with something more fitting depending on the voice type selected
- Other: perhaps the player could "talk" to villagers when trading, whimper/cry when at low health, and inhale when surfacing from underwater?
Not sure if this is too much effort for not enough gain but given the loads of mods for realism and immersion (both for the character model and environmental stuff) I'm surprised there hasn't been any significant mods like this yet.