The current chunk generator in the Bukkit API can only generate chunks using bytes or shorts to identify blocks. This means that a lot of the recently added blocks cannot be added by the ChunkGenerator alone and that you have to rely on BlockPopulators to inject more advanced blocks after-the-fact.

It would be nice if you could do that directly from the ChunkGenerator instead.

So I suggest that you add the following abstract method to the ChunkGenerator class:

Material[][] generateBlockSections(World world, Random random, int x, int z, ChunkGenerator.BiomeGrid biomes)

Another variant might be to use a lightweight Material class that holds a typeID and a data byte. Although this goes against the magic value deprecation of the BukkitAPI so the use of Material as suggested above is probably a better idea.

public class LightMaterial
{
public int typeID;
public byte data;
}

and then add this to the ChunkGenerator class:

LightMaterial[][] generateBlockSections(World world, Random random, int x, int z, ChunkGenerator.BiomeGrid biomes)