Ethereal clears every biome when it starts to get rid of the default mapgen, which breaks the nether and can cause crashes.
Adding Ethereal as an optional dependency ensures the nether is loaded after Ethereal has already cleared the biomes.
Add more appropriate/atmosphere distance fog to the nether, via climate_api mod to avoid conflicting with other mods.
Any game or server with climate_api mod installed will be expecting climate_api to take control of sky values.
