I can answer one - A lot of story line systems/jumpholes are locked afterwards; they're not really part of the active universe, they're only there for the story and don't serve much of a purpose after that. I know many mods take those locked systems and expand upon them, but in vanilla FL, there's not much there.

As for storyline mods, IIRC, there's one recently that came out called Wings of Federation or some such. Check the news archives here, there was a post some months back about it.


And welcome to The Starport.

There is also "Trent the monkey king" mod, which was the first campaign mod iirc.
It "only" features one new mission and I never played it by myself, but that one mission might be pretty large. Plus rebalancing of the old missions and providing a lot of options.

Just worth noting, as there aren't really many SP campaign mods out there.