For a Freespace MMO. Do not expect something to come out of this. It's just for fun.
For now, at least.===============
How would it work? There would be two factions: The Galactic Terran Alliance and the Vasudan Imperium.
The players pick a side, then battle with fleets and encounters that determine the faction's success on a star system.
The goal of the game is to weaken the opposite faction until an attack on the home system becomes sustainable.
After this, you would storm the faction headquarters system, their most developed one.
The game would essentially be a constant battle to
capture predeveloped infrastructure.
The more Systems a faction owns translates to: research speed, destroyer shipyards, subspace nodes, etc.
In short, the game would be a massive capture and hold space sim. (Planetside 2 represents the basic gist of it.)
After that, things get interesting:
The Shivans would be a PvE/PvPvE event. Once the war has gone on for long enough, a Lucifer scouting party would be dispatched to the GTA/VI sector.
Upon arrival they would start culling the most powerful faction, while keeping the weaker one tied down with weaker attacks.
Stars lost to the Shivans would be invalidated, all infrastructure within them is destroyed upon their fall.
The goal of the Shivans is to purge both factions.
They 'win' by destroying both home worlds.
Once the Shivan event triggers, the GTA and the VI can forge a peace treaty, which would change the victory conditions to destroying the Lucifer.
If they do not make this treaty, they will be playing against the opposite faction and the Shivans. (Hence PvPvE)
The goal to destroy the Lucifer is added to both sides, while keeping the original home conquest one.
The Shivan event would allow for special research opportunities, namely: Shields & Beam Cannons.
Research materials would be acquired through special 'Shivan raids' to get materials back to your factions.
==========
A tutorial, to introduce the game mechanics, would be one in which you play as the Ancients, just before the Shivans came for them.
An internal feud would serve as the pre-Shivan tutorial excuse.
Much WIP-ness in this. Add your own ideas!