Elite Dangerous is a million-dollar project with 100 people in it, but I think that some game mechanics would fit very well to this game
In open play
  • go to the port and get a mission from a mission list.
  • complete the mission
  • profit!
  • uses gold to buy ships, buy upgrades, repair ships, buy crew supplies
  • repeat
This "simple" gameplay keeps players on Elite Dangerous for hundreds or thousands of hours, mainly because there are some pinnacle ships difficult to get and to be proud of
additionally
  • ranks ( some ships require a rank / some ports require a rank )