In many recent updates, they have made it so that it is possible to do some mapmaking features that were previously impossible without using third party tools. (e.g. using /clone, being able to put data tags in /summon, /setblock, /give, /tellraw and a few other commands)
One thing that I have noticed that seems to be missing out is how to set it so that you can make it so that it is a certain biome.
(By that I mean that it changes the grass and foilage color and weather to whatever new biome you set it to. I DO NOT mean re-generate a new biome in a certain spot)
The command could have syntax like this: /setbiome <x1> <z1> <x2> <z2> <biome>
So it would work like /fill by converting all the land in that area to the biome (e.g. minecraft:ice_plains, or minecraft:roofed_forest, etc)
My other suggestion (which is also related to biomes and commands) is a target selector argument which only selects entities in a certain biome.
e.g. /kill @e[type=Zombie,biome=ice_plains] would kill all zombies in an ice plains biome.
Likewise, /kill @e[type=Zombie,biome=!ice_plains] would kill all zombies not in an ice plains biome.
The command would be useful in mapmaking that requires certain biomes (and a certain color of grass) in a certain location (because superflat can only have one biome in the whole world, and it is difficult to get the right biomes in the right place in default and customized.).
The biome target selector would also be useful in adventure maps to create biome-specific features within the map (such as making it so all zombies that are in ice plains wear snow on their heads, or all zombies in deserts wear sand on their heads. The possibilities are endless.)
It would be a great idea since The nether and end are both considered biomes. You could change the biome to either of them in the overworld or change the nether/end to an overworld biome and see what results you can get. I thought that /setbiome was a command awhile ago but i didnt realise the computer had world edit installed. it was my school's computer so i couldnt really know at the time.