Using custom biomes will now work with Custom-BiomeProvider
(Default Custom-BiomeProvider: BiomeProviderCheckerBoard, BiomeProviderDefault, BiomeProviderLines, BiomeProviderMultiNoise, BiomeProviderSingle, BiomeProviderSquares)

Biomes now have the BiomeDecorationPopulator which can be added with:
#addCustomDecorationPopulator(BiomeDecorationType , BiomeDecorationPopulator)
It allows to place small things like Ores but does not allow do do much stuff since it needs to be out of sync with Bukkit.

Custom Environments and GeneratorConfigurations will now work better and have more features to change stuff