What's next? I decided that adding different types of systems/planets/cities will add a LOT to the game. So basically, I have three ideas for city types as of now: pirate mall (think some pirate outpost), research station (science research stuffs) and mining colony (owned by a mine).
So in addition to inhabited systems, you'd have systems which were like, infested with pirates, and uninhabited systems would have both research stations and mining colonies scattered around.
I also thought, I should have ground defences around cities and so forth. This would be useful for pirates who can shoot you to prevent you landing at their base, until you hail them with the correct code or something.