I have a feature request for MCreator - improving the biome floors. I feel it would be very useful to be a ble to chose multiple blocks for the biome floor - an it would make custom biomes look much better. This could be created in a way similiar to the program world painter - the player can pick multiple custom and blocks and give the a chance out of 1000 for being the floor block. For example, for a taiga biome it might be 700 Grass and 300 Podzol. It also allows 2 types of generation - blobs (with changeable size) and random noise. I reccommend you check out this program and see if you can implement something like this into MCreator.