Originally posted by DarthTanyon:

"An important thing to note is that the Mistlands biome will only generate in areas you have not yet discovered. Therefore, if you have explored a lot of your world, you might be better off starting a new one in order to actually be able to travel to the Mistlands."

This is from the patch notes for Mistlands. I would assume the same logic would apply for the next 2 biomes. You've got about 9-12 months before you gotta worry about it.. but I doubt anyone here is going to know for certain.

Disadvantage to that, with the release of Mistlands, lots of old maps because obsolete because the spawn moved. As well as some of the island parts. And occasionally the location of some bosses.
When we got tar pits and frostcaves, it messed up mountains and plains for some players.

So my advise to the OP:

Start two worlds with the same seed.
Use one world to build that awe inspiring base you always wanted to build.
Use the other world to hunt for the bosses and unlock all building materials and the items you can build with them.

That way, if you do have to start over, you won't loose much at your "hunting seed", while at your building seed anything is still there.

Thorin :)