- a nation based on arabic myths/culture. Non-undead ghoul shapeshifters, 4 kinds of genies (Djinni, Marid, Efreet, Dao), scimitars, yantchars (spelling differs - I mean hardcore, fanatical infantry made of captured&brainwashed infidels), lots of (mostly light) cavalry. I'm sure someone knows the subject better than me.
- a slavic nation (100% pagan). If it won't come with Dom3, I will do my best to mod such a nation. The main problem is that slavic/pagan culture isn't described in many records, and the Church tried its best to erase it. Still, lots of info can be found. Slavic people often worshipped warlike gods (like Svarog or Perun - althrough it's not sure if Svarog was a god of his own or merely a prefix of older god Rod. In that case Svarog Rod would mean "mighties Rod" or similar). Slavic people were known to ocassionaly join raiding parties with vikings. There was a widespread belief in supernatural entities, you can even say demonology. There was lots of minor supernatural beings, many of them dangerous).
Without too much research I can say that army would be based around teams/parties of 15-20 or so people. This means not-so-great commanders.
As far as magic goes, witches were supposed to have great knowledge of charms, curses, herbalism, shapeshifting, divination, demonic pacts, and healing. Witches were often feared, but also respected, mainly because they were able to heal the sick. Translating to Dominions language - a bit of Astral magic, nature/earth, possibly Blood.
One of national heroes would have to be Baba Yaga. Capitol magic sites could include Lysa Gora (Bald Mountain), a place where witches were supposed to gather ocassionaly and meet devils (djabel), demons etc. But I don't think limiting witches to capitol would fit very well - they often lived in alone in the woods.
Nation-specific spells could be some summonings - there were dozens of demonic beings to be afraid of.
http://en.wikipedia.org/wiki/Slavic_mythology
So, there is a potential.