Grass blocks, grass, leaves and other flowers/nature items are ruined by Minecraft's biome system in biomes like the desert, it makes the blocks not so nice to look at. if someone is trying to construct a city in the desert or a build wanting to use lush green grass or leaves they cant. Take a city like Abu Dhabi for example, it is in a desert and has green grass and nice green trees. This would make the desert and other biomes more realistic. ( could add a way to add upkeep needed to them but seems dumb ). Me and many others think having a way to change what biome your block is in could encourage builders to build city's in Africa and other places now because they wont need to worry about there city looking worse because of biomes.