a sci-fi simulator (kinda like DF world simulation but on a galactic lvl) where the player can choose different starts based on the races and interstellar empires that arise in the game. there would be some defacto species and empires but most if not all the lifeforms would be procedurally generated. as it befits a game inspired by our beloved fantasy simulator, this game would use glorious ASCII graphics with the option for tilesets.
there would be 2 gameplay modes, the first one is Colonist mode and focus around the player being a citizen traveling from the heart of its starting empire towards the exploration of deep space. the player will have to resort to survive by different means not only combat but also crafting and social interaction with the beings it encounters out in the frontier, this also includes piloting vehicles or spaceships (not sure how do you manage a vehicle in a RogueLike but examples must exist).
the other gameplay option is Colony Mode, this one is of course about city management much like in Fortress mode but with the difference that you can select from a huge list of Star Systems, Planets/Moons and Alien Races or Empires to pick. apart of these racial and cosmographical options you would also be able to choose the method on which you want to embark on the select terrain. all of those decision would have an impact on how your colony will fare at the start.
i guess the game would be heavily inspired by titles like ASCII Sector, Dwarf Fortress, URR, SoH, Rimworld, Stellaris, Aurora 4X, TiTS, Cogmind and Infiniverse (a small prototype i saw on the internet years ago, it never took off sadly) and this is just for a basic idea (would probably throw SPORE, Evochron, X3, EVE and Starbound on that mix).