The game is about Civilizations and not political entities, and Civs are going to me more of a blob than some particular dynasty's Empire. The Etruscans would to most come under Rome, rightly or wrongly, as would Illyria arguably, although the region might be worth consideration for a Civ in the future, though Europe is pretty much packed as it is. No doubt any new expansions would still cram some more in though.
Ashanti were also mentioned in my list as Ghana, we already know all too well that they'll go for more recognisable names, which is understandable. It also allows them to cover a more diverse time period than simply one iteration of a Civilization. Dahomy is an option, but particularly in a classical sense Nubia is something that needs to be considered. If I could only pick one of Mali, Ghana and Dahomy though, I couldn't look much further than Mali, to leave them out for the Songhai would be like leaving Germany out for Austria.
The Huns and Mongols were nomads, yet they seemingly didn't feel the need to include it in their mechanics. There are also plenty of better options for nomads still.
Not to be cynical, but if they did have another expansion, they'd still cram it with European civs. You'd probably get Belgium, Serbia, Hungary and Italy or something like that. I doubt they'd ever have less than a third of new civs non-European.
