Pythium is Byzantium. That strange hybrid lovechild between Rome, Greece, and Turkey.
I'd be curious to see a nation themed around Aboriginal mythology, from Australia. I know very little about it, but it seems to have an interesting flavor.
Also, a Native American nation that perhaps had things like the bear tribe and deer tribe recruitable in their castles, with a late game that revolved around various totemic animal spirits, with Coyote being one of the most powerful, and needing high Astral, of course.
My favorite that I would like to see though, is something based off of the Sumerian Annunaki. Some believe that they were alien visitors, and the mystery shrouding the mythos makes it very compelling to me. The Annunaki were said to be giants (not huuuuge, but say 10ft tall), and had godlike powers with which they ruled the Sumerians. The stranger websites claim that they educated humans, and they were the reason that we developed civilization, in exchange for using us as slaves to mine gold that they needed to repair/fuel their spaceship and get off of this planet, or some such thing.
It's pretty far out, but even just using the stuff that we can reason to be true, it's very interesting (and no reason not to include hints of alien visitation, it's fun!).
Anyway, the wiki has an interesting taste of it, unfortunately the only websites I have bookmarked, are kind of crazy. >.>
http://en.wikipedia.org/wiki/Anunnaki