One thing I think would be really cool is to allow people to upload structures they've built and then have an option in the game to randomly populate the landscape with them. I know it's already possible to import structures (.structure files?) but to have it done automatically and at random would add some interesting variety to the game.
Given its focus on online community, it seems like a no-brainer feature. Having some options for world generation would also be nice. Maybe checkboxes for what biomes you want to have, what kind you want to start out on, whether you want random structures, etc. That's probably my main gripe with the game: the lack of customizability. I assume that will happen eventually and I'd sure love to see it.