Nether Biome Features for Biome Generation

Currently there's only overworld things like taiga rocks, meadow vegetation, dripstone features, lush cave features, etc.

I think it could benefit from Nether generated features, such as crimson/warped trees, soul sand valley basalt spires, basalt delta formations, etc., especially because you can't try making custom trees for custom Nether biomes with nether tree blocks, since custom trees can only generate over dirt and not nylium.

Also, giant brown mushrooms and giant red mushrooms should definitely be added to the dropdown list of vanilla terrain features. They would spice up biome customization a lot.