It's been stated since the first game that the citadel is just a massive portal that links to dark space. Since there must be a type of space station in dark space this gives me an idea for a whole new game.
The game would be set after the Reaper war once the damage has been repaired. Wanting to find out what lies beyond the galaxy the Council sends a team of Special Forces soldiers to find out what lies there. Using information from controlled / destroyed Reapers they use a prototype starship with greatly increased speed to find this portal / station in Darkspace with the goal of possibly getting more technology.
The ship would set off on towards the edge of the galaxy in the opening cutscenes and have one of those dramatic scenes were the ship heads into Darkspace. You would then get to know your squad as well as the people on your ship through conversations. After you do this the screen cuts to black and says "some time later" and shows your ship arriving upon a massive station. However from the start things seem very ominous, already your special communications network won't connect you to the alliance. Your Commander knew this would possibly happen and tells you and your squad to board the station. This begins a survival horror game. If any of you have any ideas post them, what would the enemy be, how bad does the situation get?