A 2D space game that allows different play styles like trading, piracy, joining a faction. I imagine it as some sort of space ship simulation with rather big crews with needs. Ships start from small, one man ships, to ships with crews of about 50 NPC's and complex design. Ships have then different departments like a bridge, crew quarters, engine and cargo. All of which need to be managed by crew members who themselves have needs like food, mood, money etc. money might not be an issue if you join a faction.
the key mechanic is basically crew management. As the Captain of a spaceship your task is to manage all the needs of your crew. That means having enough food, rest and keeping them happy in general. But the things a crew wants will strongly depent on the type of leadership, for examples a pirate crews will want to be paid but don't need a lot of free time or good food. On the other hand a crew from some sort of federation ship will need no money at all since they aren't hired by you, the player, but the federation instead. This crew won't be proven in battle though and might need counseling instead. the activities of the player will not only shift with the play stile but also the crew size. Managing a schedule for 100+ crew mates might be tedious so tasks like this might fall into the hands of an officer and instead the captain is now obliged to schedule social gatherings. Each and every crew member will have a designated post and schedule and depending on their experience will handle his/her tasks with variable efficiency. The events, like battles, traveling from A to B will in general be handled by the crew and the player is "only" giving orders.
The Player is the commander of his/her ship. He is free to trade, attack or do whatever is possible in the limits of the game (hopefully pretty much everything). Depending on the players choices he will be known as trader, pirate, law enforcemend. These also strongly depend on the faction the player is affiliated with, if at all.
Ships should be completely explorable for the player and also manageble with specific UIs. A little bit like a city sim. The Ship should have every necessity it would need tu run like energy systems, engines, weapon systems, crew quarters and so on. I'd like the player to be able to make interactions with every single crew member and every crew member has a designated role on the ship. If a crew member in a cruicial position falls out, others will have to replace them if there are any. Depending on the evailability, stations will receive a penalty because other crew members might not be as proficient as the designated one and their designated functions will be abandoned.
A rather unconventional idea would be to just give orders and have your crew execute them depending on their well beeing and skill(a nice rpg system for skills could work well gere). This would be close to actually commanding a space ship. I fear this might get boring to quickly or be unsatisfying as you can't put in your skill as a player.
The universe consists of systems with different opportunities (different levels of danger, different goods etc.)