How could they do a flight simulator DLC? That would include flying airplanes, and that wouldn't work due to the game engine.
In a way I think it could be possible.
Make you 'fly' using the system bloatflies and Cazadors do.
Like how Op Anch strips and gives you in sim gear, the game gives you an unremovable quest item that gives you an airplane skin. (Item is removed via an extensively tested script to make sure it does not fail to remove it.)
Various clouds with invisible walls on the ground so you can 'fly' with a low resolution city background texture below.