Originally posted by Fzanco:

Yes we know the poi updates with the explored parts etc, but there is no solid info on what happens to those completely empty biomes if explored. Unless you got a link to a dev or something no one actually knows what will happen map generation wise when mistlands is implemented or any other empty biome for that matter

You are new here ? That will act like mountain caves and tar pits , will not be there if the place actually was explored, works in the same way , thats why people with old seeds that already have the old mistland placeholder ( big trees and skulls ) explored didnt get changed for the new placeholder