I like everyone of them, exept the Fungi Biome and the Darklands... Those seems very unrealistic and makes whats Minecraft not Minecraft... (If you see what I mean )
The question is, what makes the existing mushroom biome more Minecraft than the fungi biome?
I'm not really buying arguments saying something isn't "minecraft-esque". Because in most cases, it could likely be something Jeb would implement, and suddenly people would have a completely different view on the same topic.
I've been meaning to do something like this, make some mockup biomes, but I got disgusted with Minecraft and gave up on it for a while.
Anyway, the effort you've put into this is great. The mushroom cave is seriously just awesome. More subterranean biomes would definitely be awesome. Some of them, like the frost biome, look a little boring, but I can appreciate that you've bothered to put snow into all of the textures.
If I can manage to remember my Twitter, I'll make sure to be one of those annoying idea guys spamming the Minecraft team, specifically with this.
Great job on the pictures. Out of all of these, I like the tropical/desert islands, the "wild west" type deserts, and the savannah. The others seem a little unnecessary or out of place. I'd love to see functioning volcanoes on desert island chains though. Savannahs would be a great place to see a whole load of new wild life mobs.
But as long as we're adding more biomes, why not make it more realistic which biomes can spawn next to one another. Such as: Tropical islands can only exist when surrounded on all 4 sides by ocean biomes. Or tundra/snow biomes can not spawn next to deserts or jungles. Mountain and plains biomes are much more likely to spawn next to "wild west" deserts, where as savannahs and mountains would spawn next to normal deserts.