Jens Bergensten has recently revealed that Minecraft will soon be changing its map format which should allow for easier modding of the indie title.
The new map format which has been nicknamed “Anvil” at Mojang will raise the building height by a factor of two, to 256 blocks. It will also change the way data is recorded allowing mods to add new blocks and tweak biomes. “Anvil” will be first released in the next snapshot and then officially in Minecraft 1.2.