Ok now I don't think this is ingame yet so here it goes. Colonization. I think would be a cool expansion of the game since you can already find new systems and planets I think it would be cool to be able to set up colonies which eventually can turn into cities and such. This would add more pvp and pve as well since the colonies can be attacked and even destroyed. Space stations as well for people that find that breathtaking view is a sector of space.
Space stations of course would be more expensive and more to manage.