I would like to request a mod that adds a new world type: Sky
What that would do is make all the Dimensions generate like the Skylands, the Over-world would be the regular Skylands, the Nether and End would also generate like that but with their dimension blocks, i.e the Nether would have netherrack sky islands and would generate Fortreses, and for the End, it generates islands of endstone and Ender Crystal pillars.
End Example :
None of this mod adds new blocks or items and is purely generation, so it could possibly be easy to make.
This sounds like it would be a simple idea to implement but it wouldn't. You'd need to overhaul the Minecraft world generation code completely.
The main problem with this is that it means it will be incompatible with every single mod in existence.