CarrotChompsreported this suggestion
The ability to define a ChunkGenerator in the config that creates chunks of a certain Block Type from the bottom of the world, up until the surface of the block reaches the bottom of the procedural dungeon starter room. Then the rest above that surface is air. Either that or allow for the chunkgenerator support super flat preset code format. https://minecraft.wiki/w/Superflat#Preset_code_format