1. Eyes could water from sand or ash getting in your eyes. Could be disabled by default, but enabled for harder packs. Maybe helmets, for simplicity, would act as protection against this visual effect?

2. Player could slowly accumulate dust over their body in wastelands, and sand in deserts. This effect would cease if the player is moving

3. Random coughing for the player + villagers, illagers, and other such NPCs in wastelands

4. Heat haze, although I suggested this... last year.

5. Warm biomes, in general, might attract mosquitoes and flies to the player (represented by the sound of a fly buzzing near the player at random times so as long as a player is in such a biome)

1. I thought of adding an overlay that tweaks the view based on environmental factors. Some mods do something similar when the player gets damaged (like tint the screen red or use a vignette to get the feeling of a tightening view). Also thought of adding view changes based on the helmet being worn (again to change perspective) - similar to what pumpkin blur does when where a pumpkin in the helmet slot. My main worry about doing this type of thing is somehow affecting gameplay.

2. This one is interesting. Could also add effects for swampland where crud collects on the lower extremities, or in snow biomes where clothing gets snowed up.

3. I have been thinking of adding per entity sound effects. The idea you have here is an interesting one. Though I may draw the line at having cows fart.

4. I've been looking at this one, as well as ground fog. I am reading up on both topics to see how shaders can be used to do these things.

5. This falls into the same category as 3. I have been thinking of having flies fly/buzz around zombies and your suggestion here is an extension of that.

Not sure if you noticed the code churn i the code vault. I have been doing a lot of refactor work to make effects entity centric. My goal is to come up with a framework where it would be easier to add per entity effects.