I'm a Dr Who fanatic (I don't suppose there's a *good* way to put daleks in the game?), but I think this theme could go much, much deeper. Have you ever considered a blood nation offshoot of Agartha? I'm reminded of the vast, spectacular stoneworks of middle America-Maccu Picco being the "flagship" of all that.
Is it possible that, deep in the jungle, a few Agarthans may have survived and come into contact with some lost civilization like the Olmecs?
The humans might worship the Agarthans as gods on one hand, but be influenced by Mictlan, on the other-leaving Agarthans in the uncomfortable position of being in possession of lots of sacred blood.
Maybe not even MesoAmerica, maybe instead an Easter Island scenario-we don't have too many island-based nations, Haida (not counting the ones based on British myths) is about the only one. Maybe a civilization that always starts on an island and only has limited access to amphibious troops, as a buff?
Speaking of British myths, the stones of Stonehenge were believed for a long time to be giants who had been transformed into stone by Merlin. It'd be great to see a nation based on Anglo-English myths that wasn't overly influenced/corrupted by Saxon, Frank, or Celt conquerors.
Maybe a Welsh nation?
Also, there's a legend, not sure where it comes from, about a castle where a massacre of it's residents took place, and the murderers buried the corpses of the castle's inhabitants under the stones of the castle's floor. So, while the conquerors were having their celebration feast, the stones of the castle, themselves, rose up and struck them all dead, in very gruesome fashion.
http://enews.ferghana.ru/article.php?id=1345
this link should take you to some very weird/intriguing, photos of supposedly natural stones in a place called "Devil's Helmet", in Uzbekistan-apparently, it's a very bad-mojo place. Might serve as inspiration for artwork.
P.S. I haven't had the chance to try out your mod, due to my personal computer's hard drive exploding in spectacular fashion.