We get 12 Sovereigns so the 6 Mithrilar part isn't accurate anymore.

And in before the scoutdog, Frogboy reuses many ideas of Galc Civ 2. Or better said, many ideas he had before he started Gal Civ (1). As how far he is reusing and/or redefining... who knows. Most probably it's just some kind of parallel universe to that of Gal Civ (in the best of cases), as from some of the background information of Gal Civ and the stories Frogboy shared with us, Draginol could travel through dimensions or something like that. I'm not going to define it as franchise reboot (quite popular these days, be it Galactica, V, Star Trek...), as I do believe that they are just preparing the Lore properly for extensive use in future games (the rpg, maybe Societies could be based on it too?...).

12 factions (6 human kingdoms, 6 fallen empires), each one with a Sovereign. Multiplayer is a different beast in which factions can be used by more than one player (I suppose).

My reference to 12 Sovereigns was about the story not about gameplay elements (beyond the basics provided by Stardock for single player campaign).

We will be able to create our own factions(and Sovereigns) so I don't see any reason why AI couldn't use them for solo games.