'Deep Underground' Zone (Part Two of Two)

And maybe, monsters that spawn on Hardened Stone would be slightly buffed, or more likely to have armour and weapons, Making caving much more of a challenge. On top of this, perhaps as you continue to go deeper, there would begin to be a slight haze effect, which slightly reduces how much light is emitted by light sources, and reduces view distance.

Another mechanic to develop the deep underground, might be that all normal ores (Along with a new one or two, maybe?) can be found in Hardened forms, which would only be smeltable in a blast furnace. And probably diamonds would only spawn in the Deep Undergound zone, making it more difficult to get, whereas now you can get diamonds in less than an hour after creating a new world, provided you have a bit of luck.

I don't know how well this would fit with Mojang's plans for the Cave Update, but I think think this would add more danger and depth (literally, and figuratively) to the experience of mining and caving.