Sub-Biomes

Individual Biomes in Minecraft always end up looking pretty similar to each other. Every forest looks the same, and every cave has the same spread of ore. What if every individual biome had little variations within them, without changing them them fundamentally. This my the idea of sub-biomes. Sub-biomes could be as simple as changes to the amount of trees in forested biomes, or more complicated things like making some areas in caves have more ore or less ore. Although this idea would likely be very difficult to add, it would definitely make the world much more lively.l and interesting.