You forget the most important thing: customers and their money!
Spain is a market of 46 millions which would surely love their nation to be playable. I don't know whether south americans identify with spain, but that might even increase the number.
Vikings might fit for scandinavia, but they are only about 25 millions (S,N,Dk,Fin) and don't identify themselves with vikings that much any more (I lived half a year in Nidaros - old name for Trondheim! - and there's not so much to be seen from viking history, really nice place by the way

)
Furthermore, the vikings would make an excellent barbarian city state, which would explain their appearence in the video (offensive, but good trading partners if they like you, and mighty allies!)
Persia won't attract too many players, or is there a huge fanbase in todays Iran I missed? Historically, both were major players, but spain more recent, persia mattered most 2500 years ago.
Sure I could be wrong, but spain would be the only major market not served:
USA
Germany
France
Italy (Rome)
GB
Don't know about the asian fanbase, what about korea?