You get it all wrong. My reasoning has nothing to do at all with Eastern Europe looking all the same, it has more something to do with Forgotten Empires past approach.
You know, every single architecture set is represented usually by roughly 2-4 civs (with the notable exception of Indians but we’ll get later on that point). Adding more Eastern Europe or generally speaking additions in architecture sets with already 4 civs in it creates redundancy, especially considering that in the original game design Ensemble had, the civ names were rather vague and could encompass a lot of things. It has its downsides like you can see with the Indians civ but it’s definitely useful to design civs. Saracens could be a dozen civs too, you know?
Usually, DLCs are released around a theme (Africa for AOK, Central Asia for TLK, South East Asia for ROR). Adding more Eastern Europe would feel weird and to some extent even redundant. I’d say the same if they’d add more Vikings civ like Danes or Sweden which would be from my own POV pointless and redundant.
Yes, they added Burgundians which kinda is a Franks civ split and Sicilians (which I really don’t get as a civ pick (they’re basically Normans without being named Normans), but that’s the exception and not the rule.
Eastern Europe has a rich cultural history on its own (e.g. Corvinian Reforms, Slavic Mythology etc. to just name a few), though adding more of it IMO would feel as redundant and to some extent unnecessary like adding Danes, Swedes, Austrians, Bavarians, Swiss,. … when there’s still underused architecture sets like Indians which is like putting all Europe under Franks.
I should probably take a break until we know more about the two SteamDB DLCs I hinted at in another thread. We’re speculating in the void IMO. They’ll tell us soon enough if it’s an expansion.