Im not sure if i will need to make a mod for this or what, but i figure i will start here for help.
I am trying to create a world that has no true surface, so the land elevation will surpass 250 blocks high and will have ocean above it. And within the ground will be huge monstrous ravine and cave systems large enough to grow trees and such in them. So basically, it will be like hell is, but in the over-world and not the nether. This biome/world seed will have lava lakes, and water lakes. And it shall also have animals spawn in them, so cows, sheep, pigs, rabbits, chickens, and any that i may have missed.
So really, everything thing about the over-world, formatted and within the nether a place that feels like the nether. Water had to work in it too. I feel if it is possible for someone to make this biome seed/mod that it will be the best minecraft experience ever, true minecraft survival.