Originally posted by Ryzilynt:

But it may potentially add new spawn points, i.e. onions or dark wood.

My answer is focused on the part about new biomes in the OP, but you're probably right about that.

I imagine that new resource spawning won't be a problem since some resources already respawn during gameplay, but I think that the map/ores generate only at first load, which could cause an issue for an entirely new biome.