Since rail systems are here now, I want to add to this discussion, that I strongly dislike the necessity to have a ship core on any docked entity. This prevents anything cool with a gun on it being built. I'm not talking about turrets here. Imagine this: you have your huuuge ship with large compressed guns stored on the inside. When entering battle (or really just showing off) you press a button and suddenly huge gates on the sides of your ship open up and your weapons come out and once they're out, they expand in some cool way to their full size.. and all that only realized with rails!!
I don't want to have Bobby controlling those guns. I don't want to enter a different ship core to use them. I want to feel like the captain of a hardcore battlestation and stay in the cockpit.
If you take the core out of the rail system and made it possible to just build stuff on rails, that would make it a whole lot easier to create automated gates or expanding areas or whatever one could think of...