But which biomes are we actually missing?
Isn’t that a Roofed Forest above Kae’s place? There’s a Flower Forest to the west of that. We even have a Bryce Mesa (the Monument Valley type). There seems to be a Mega Taiga in the North West, above the large Jungle.
I haven’t spotted a Sunflower Plain or Birch Forest, but they wouldn’t be that obvious and I’ve probably missed them. I can’t see an Ice Plains Spikes or a Mushroom Islands, but it seems to me that it would be very difficult to find a seed for a world the size of ours that wouldn’t have a couple of biomes missing.