I think he said it was going to be based around the history of Altaria
The info Vandenburg collected earlier in this thread mentions the Mithrilar, which is an Altarian thing. I don't think it is so much an extension of the GC universe as perhaps a sort of prequel or alternate worlds thing. But I'm probably projecting because I'll be pretty disappointed if the maps are on a spherical planet or planets in star systems that are in galaxies, etc.
If you go to the GalCivII website, click on databanks, and then click on GalCiv Universe, you will find quite an interesting story. Here is a taste or two:
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The first 3 books outline the Drengin war and introduce readers to the mysterious Arnorians (the Arnor).
The 4th story, Twlight of the Morningstar, tells of the fate of one Arnorian who was helping the humans. The last two stories deal primarily with the Yor and tie the rest of the stories together, introduce the Iconians and Thalan and resolve the various plot lines. I won't go into too much detail on those because Galactic Civilizations III will borrow heavily from those particular stories.
Do you play as the Thalan who have come from the an alternative future that exists in the Galactic Civilizations III timeline and snuff out the Terran Alliance before they destroy the universe?
Ironically, this story is told as a story by an Arnorian who is found on an alien world called Altaria. A cataclysm had occurred and changed all of existence and the dark Mithrilar, called Draginol (that's the source of my on-line handle btw), was also on Altaria.
The second two stories deal with the Altarians trying to resist the evil Draginol and his forces and the aid of Mascrinthus, the last surviving Mithrilar other than Draginol.
The ending of this actually sets in motion the original stories creating a loop.
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These little nuggets have been sitting there since I first came across this game a few years back, and yet we failed to see them, I only saw them when I was trying to figure out who the Xendar were.