This is a hard question.
First thing is EVE. I really like the mechanic that everything in the universe is created and run by players. But on the other hand the game should be also playable singleplayer (like the X series) or small groups on small servers. Don´t get me wrong. I don´t need a story or anything like that. It´s more about beeing able to enjoy every aspect of the game with just a few people.
But what I think this game really needs more, and Spock forgive me that i have to compare it, is damgerous places like the nether in minecraft. Places you only want to be with your titan. Places which make it necessary to build powerfull ships or use good tactics. And of course going there should be rewarding.
A survival aspect as mentioned above would be nice.
Adding a better trade and storage mechanic would also help to get this game to the next level. Every storage module should need a space attached which determines how much blocks can be stored and if there are blocks stored it increases the mass of the ship. This would add a serious logistic element to the game which created a lot more depth in gameplay. Mining -> Transporting to Factory -> Producing Blocks -> Transport to Shipyard -> Build a Blueprint. This would be heaven.
It´s a hard task to get all the good mmo, singleplayer and sandbox elements in a voxel game. Schema does a good job and i see this kind of things come to life.