Please read the pinned post on creating new biomes and dimensions. Remember that individual items, mobs, and structures should still go in their own categories - this is not a category for entire updates.
Biomes and Dimensions
Vote for an existing idea or New post
Large biomes /Amplified Worlds needs info
Wastland biome needs info
Update Magma needs info
Corruption/ badlands/ dark lands needs info
Unnamed Dimension (with Blazes) needs info