Here's a campaign and Shivan theory bundled in one, but I'll probably never make it, especially since I am devoting so much of my free time (and also some of the time I should be working) on the FS-TBSG (This also works in the Gangelas models (remember those models starting with G, like the GD Deva, GF Thirst, GC Yllabia, etc.?)):
The Shivans aren't just xenocidal, and they have other plans besides wanting to get rid of us. Their main goal is to create an inter-universal tourist-trap. Making Capella go supernova was just a step towards creating an enormous habitat for a more powerful race that they or their creators (this theory and campaign does not attempt to answer the origins of the Shivans) hope to use to trap "tourists" from other universes in our own, so that they, their creators, and or everyone in our universe, or something, idunno what, benefits.
Note: there is physics stuff that suggests some of this stuff, but not much of it, might be possible.
This more powerful race they are building the habitat for is the Gangelas. The Gangelas build a gigantic structure to absorb the galaxy and turn it into a tourist trap which will capture "tourists" entering our universe from the universe(s) that our universe formed out of (from a black hole (there is some physics stuff to support this, but i am very likely misusing it)), the technology to travel between universes not being much unlike the technology to travel in subspace, just with different variables in the equations, or rotated, or something. But you have to be close to a black hole to do it, and yet far enough away not to get sucked in. Oh, and then do the same with the whole rest of the universe, bit by bit, over billions of years.
The Terran/Vasudan objective is to stop them before they get started. If it's a multi-chapter campaign, the first will be the GTVA (or whatever it has become in the future) fighting the Shivans to keep them from blowing up the final star they have to explode to introduce the Gangelas into our galaxy/universe/everywhere. The second chapter would be the GTVA fighting the Gangelas, and doing miserably at it. The third and final chapter would be set much much later, with the GTVA exiled to the farthest reaches of the galaxy or something, and the Gangelas continuing to expand. A superintelligent entity has been ensnared in the Gangelas' trap, and it is being subdued by powerful psychadelic/hallucinogenic chemicals produced by the Gangelas hive structure. Anyway, a less intelligent species being dragged along by the superintelligent entity (unnamed) realized just in time that their host is being captured, and they fight their way out of the Gangelas hive. Then they team up with the GTVA and kick the Gangelas out of universe again somehow.
The End.
No, I am not drunk.
