Advanced Surface Rules & Depth for biomes to generate

For now we can only edit a biome's ground, half-underground and underwater block. That means, we cannot get a surface generation with more layers such as the sandstones in the desert, and we have to use features to imitate that. Also, all the surface generation is done overground, and there is nothing we can do with the cave surface. However, these are all possible in hand-written Datapacks for custom dimensions, through Surface Rules.

Therefore, I suggest to include a Blockly-based Surface Rules editor for biomes, while the simple ground-underground-underwater type could still be an available choice.
Also, for now, we can only have underground biomes in the overworld. By letting the modders to edit the depth for biomes' generation, this can be made possible in custom dimensions.