I personally believe after a while, Minecraft's biomes get repetitive. Some may not agree, but i think there should be more realms and biomes. Here is a video with 5 pictures of my ideas -
The First one is sort of a mountainous area, or an area near a desert. Here, a mob called rams spawn, as well as cows. The orange earth is a new kind of dirt, similar to the 4 types of wood.
The Second is a cliff. Rams spawn here as well.
The Third is a kind of field, or plain. Sheep and cows spawn here.
The Fourth is a marshland. I can not find any mobs that are currently made to spawn here, so i think there should be some sort of fish.
The Fifth is a special area of peace. Here, sheep, pigs, chicken and cows spawn here.
My sixth idea is an Aether, an opposite of the Nether. I realize it was already created into a mod, but i believe it should be part of the game.