These 4 biomes, including 3 exciting new biomes, are EXTREMELY rare. I've generated several creative worlds and explored a prodigious amount of territory (thousands upon thousands of blocks in each) and I have never found a Mesa or Mega Taiga biome (except when given a seed by YouTube video, for example) and have found very few Jungle and Ice Spikes biomes. I understand these biomes are meant to be rare sections of each of the 4 biome types, but they are MUCH too rare in my opinion. If they take hours of exploring to find in creative mode, the chances of finding them in survival are miniscule, so PLEASE decrease the rarity of these biomes drastically ASAP. On a related note, I also believe the biome size is too large in general. They seem several times larger than 1.6 (and earlier) biomes, which compounds the issue of trying to find exciting new biomes be exploration. If people wanted biomes that big, they could always choose the large biomes world type. As it is, that world type is just a pain because biomes can be literally 1000+ blocks across.