Recently nexon released a post about feedback and how they could improve the game. The survery has ended but I want to mention two more thing.
1. Link Skills
Link skills can only be used in characters in the world that they are in. I personally think nexon should change it so the link skill can be used on any character despite which world it is in. It could save time as some people purely make characters on a world for just a link skill even though they have the same character in another world.
This one is iffy for me and not completely sure on this one. Storage is only shared between worlds. But it doesn't share storage with a world in an alliance. For example, Nova and Chaos do not share the same storage space despite them being in an alliance. This could help people who want to give stuff to other accounts but their in a different alliance so their storage isn't shared. Which makes them trade with somebody else or drop the thing in the corner of the free market places( stupid, but it would work). But storage space could get crowded since you only start out with 4 storage spaces unless you get more.