three dimensional / cave biomes

Biomes have generated in two dimensions since the game's inception. Though there is a temperature element, which correlates to height, that is the limit to height-based data / phenomena. Stratified distribution of ores, features, and so forth makes the entire world much more predictable and farmable, but lacks variety and intrigue.

Instead of the world generating with 2d noise, perhaps a third dimension could be included - at least for biomes and features. Surface biomes could be determined by subchunk and block, rather than chunk and x/z coordinates. This may add computational complications, but would allow for three dimensional biomes and biome-specific cave generation.

With this method, biomes which are related to each other can generate nearby without climatic inconsistencies (such as ice plains generating next to jungles), and would allow for caves with intermediary / distance-related characteristics. For instance, take three biomes of some size next to each other, left one cold, middle temperate, and right one hot. All three have a cave system running through them. Caves near the surface of each biome would have a temperature closer to that of the surface, and would have a similar temperature depending on distance from an opening to the surface, whereas lower caves without surface entrances would be warmer (as they do in real life). 

I'm sure others would agree: 3d / cave biomes are a good idea.