First of all I absolutely love the current map generator with all the sliders for different biomes. It is fantastic tool and I once made full snow map that had beautiful winter lakes and snowy mountains (though it still had some pine forest areas generated here an there even with 0 % setting and it was awesome).
What I'd like to see in the future is that you could alter the locations for different biomes. For example you could pinpoint the snow biome to be generated in specific direction (like east) and desert biome in the opposite direction (west) or leave it as random. I always try to generate maps where snow and desert biome are not adjacent (for better immersion), but it's very hard to have such map. Or at least I don't know how to without setting the other or both to very small percentage and even then it doesn't work most of the time.
What I'd like to see in the future is that you could alter the locations for different biomes. For example you could pinpoint the snow biome to be generated in specific direction (like east) and desert biome in the opposite direction (west) or leave it as random. I always try to generate maps where snow and desert biome are not adjacent (for better immersion), but it's very hard to have such map. Or at least I don't know how to without setting the other or both to very small percentage and even then it doesn't work most of the time.