Look at this:
https://www.reddit.com/r/RimWorld/comments/83flgg/world_map_generated_a_near_carbon_copy_of_africa/
I think a proper world map / planet earth map would be absolutely brilliant to play on.
In fact, is there any scope for custom maps at all?? I'm sure people would love to play on a middle-earth map or any other custom map people might think of.