Just wondering because there are areas on my world that I have left unchecked purposely as hoping that when the 1.9 update is released the ungenerated area will turn into a new biome. More specifically the mushroom biome. However, will those new biomes/terrain changes make it into a pre-1.9 world or will we have to start a whole new world over to get the new terrain updates?
As far as I know, it's just like it's always been: Generate new chunks by walking to new places on your old map, and provided you're using the new client, it'll generate the new biomes etc.
Thanks in advance.