First: I know no technical details about the game (not really interested, except I'd started working with Frontier). But I have > 10 years SE expierence.
While it is possible to make applications that modify itself, this technique is today not really used any more (similar to procedural techniques that change the game itself when being run at the first time). Game Data itself can be completely transfered to your PC. I see no technical reason why it would not work.Or is this to do with your actions in a mission producing several outcomes which have to be catered for and changes made accordingly, but again what can One Pilot do to influence the games structure.
But I would not expect that for "Offline" the changes that happened due to "Online" gameplay are even transferred to your PC.
Also I would not expect the Game Data to have a huge size due to the procedural techniques used in this game.
I think you could install a server on your PC and use it as Offline-Database. As you are only one single person playing the database should not take that much additional processing power. Most power is required for the client. Even having a large database you only access a very small portion of it while playing, so the most parts of it will be only on your "disc" (SSD/HDD).The System information is already decided, I believe, when the current Galaxy is initialised otherwise we would all find different things in the same system. So that would not be a big thing to sort out.
So what is the difference between Solo and Offline except the physical connection?
What makes it impossible to have a separate offline mode?