Long post alert (TLDR: What if Sol went to hell?) - The following is a tentative 'universe outline', feel free to steal it and make a mod out of it.
I've never really posted or shared this yet but figured I should seeing as I'm not apt to go take this mod idea and actually create it (well maybe, but not yet).
I noticed a common theme. All of the current to date campaigns involving a return to Sol involve returning to a Sol that is in some state of, well, normalcy. In BP you have the UEF, in Inferno the EA, and not sure what Blackwater Operations was going to do.
In any event, I remember reading the FS2 tech room about Earth and noticed that nobody had explored the question of returning to a Sol which had collapsed into utter anarchy.
The premise is that the GTVA returns to Sol to find a Sol system ungoverned.
Warlords, factions, civilian militias, pirate bands and individual nation states now rule the system. Remnant forces of the old GTA who still believe in the Shivans' return maintain a base on the outer edge of the system near Saturn, but are under constant attack by raiders looking for resources.
The GTVA enters the system to find a cacophony of communications traffic, a hundred nations all screaming to be heard and sided with. Shocked by the state of affairs in Sol, the GTVA moves to establish itself as an enclave of stability, only to find itself under attack by independent factions who refuse GTVA rule. The player is thrust into a climate of anarchy and chaos.
To restore order, the GTVA adopts a plan to rally people to their cause by becoming the most desirable faction to join in the system, offering relief aid and supplies previously unavailable to Sol ... so long as the receiving factions ratify BETAC and join the GTVA.
As the campaign progresses, you are Alpha 1, sent in to preserve the treaties being signed and help protect the GTVA's efforts. Your primary antagonists will be:
1. Pirates and other fiercely independent militias refusing to join the GTVA
2. Nations which refuse to join the GTVA
3. Deceitful groups which 'accept' BETAC in an attempt to hijack GTVA ships and equipment, or Groups which join the GTVA and then change their mind later
4. Anti-Vasudan forces attacking the "V" in GTVA
5. ????
Your primary objectives "in this theatre:"
1. Protect all civilian lives per BETAC.
2. Protect all GTVA assets.
3. Reduce strife in Sol system.
Common themes:
- Prepare to get backstabbed a lot. Trust nobody.
- How do you identify a civilian vs. a combatant?
- How do you win over people when all you've got are comm channels, supplies, and guns? (answer: all of the above - you just have to figure out what they want)
Oh, one more thing. I got just one rule for this "Crapsack Sol" idea:
NO SHIVANS. Having them just makes it too easy to get everybody to rally under the GTVA's banner.
On the other hand, the SOC using FAKE Shivans to scare people into joining... heheh

Do discuss this idea - I'd like to read the comments.
I just figure, we've seen so many campaigns with 'stable' Sol systems, it'd be interesting to see one where the place is 'homewrecked' and restoring order is like pulling teeth.
</end ramble>