Well, Radiant’s already promised us a glacier biome, complete with igloos etc (KS stretch goal). Oh, and they’ve also promised seasons, which will be good. So… hmm. I think I’ll start with some thoughts I had on better Minecraft biome generation:
- Slap a 1-block bedrock floor down.
- Add a few bedrock “bumps” to this, so it doesn’t appear totally flat as you dig down.
- Generate biomes. Position sensibly - no tundras next to deserts etc.
- Generate basic landmasses, plus ores. Mountains, plains, oceans, etc. Some overlap with biome generation here - can’t very well pop a mountain range in an ocean biome after all.
- Add ravines. Biggest landscape scars first.
- Add strongholds. Shouldn’t intersect ravines.
- Add in mines. Shouldn’t intersect ravines or strongholds (well could, but Minecraft handles that poorly).
- Dungeons, caverns, liquid-filled caves: they’re up next.
- Drop terrain: check to see if any sand/gravel can fall. If so, drop it.
- Water: add it to relevant areas.
- Plant life: Add.
- Mobs: Add.
I think that doing the above will give you pretty good results as far as the look of the game goes (no? thoughts?). As for biomes though, I think we should really split it into two categories: biomes, and terrain features:
Biomes
Glacier: Ice, ice and more ice. ALL bodies of water freeze over in autumn, winter & spring.
Tundra: Covered in ice during winter, sometimes patches of permafrost all year round though.
Cool Temperate: Think UK & northern Europe - snow in winter, chilly autumn, wet, etc.
Warm Temperate: Think Italy or Spain. Snow in winter is rare. Ideal climate, especially for newbies.
Tropical: Hot most of the year round, never snows, very wet. Diseases a-plenty.
Savannah: Hot and dry, but full of life. Wildfires are a danger, as is water. Monsoons are fun.
Desert: Hot and dry and basically empty.
Ocean: Big, occasionally with islands dotted about. Storms are a real threat.
Terrain Features
Lonely mountain: All by itself, surrounded by much flatter land.
Ravine: Shortcut to the depths. Just, you know, climb carefully…
Riverlands: Big river splits into many smaller ones before reaching the sea, or perhaps many smaller ones join a big one. Very fertile.
Volcano: Doesn’t need to be the active kind. Yet…
Plains, mountain ranges: forests, rivers, lakes etc: Yeah, at this point I’m just listing really obvious stuff 
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Mind you… when I say “mountain ranges”, I really mean ranges, and not something I can scroll over in a few seconds. Honest-to-god mountain ranges, complete with hidden valleys, towering peaks and such would be far (far!) superior to regular game-style mountains you can cross in 30 seconds.