I liked the variety in these older DLCs - we got a little bit from every part of the world, everyone was satisfied.
The first DLC focused on a specific region was Rise of the Rajas - from this point on, the DLC started to focus on specific regions / cultures.
For this reason, Western European and Eastern European DLCs should not cause irritation or amazement.
Rise of the Rajas focused on Southeast Asia, the Last Khan on the Turkic peoples (Bulgarians are the Turks who mixed with the Slavs and Thracians) + Lithuanians, while the Lords of the West focused on Western Europe. Since there is Eastern Europe now, it is logical that the next DLC will concern a different region of the world. I bet on the African DLC.
I hope DotD will add at least 4 new civs to us. If it’s only 2 civs, it could already mean the era of small DLCs (2 civs and 2-3 campaigns) and they would be expensive. Besides, other games in the series could have the same DLC policy. African DLC is heading to AoE 3, probably better if there are more civs than just Ethiopians and Hausa? So I hope that all AoE games will receive solid and well-made DLCs.
I hope that these DLC will receive 4-5 civs (Poles, Czechs, Serbs, Croats and Finns) and campaigns for these civs. New architecture style - Northern European for Rus (currently Slavs), Vikings and Finns.
The next DLC (I do not write that it must be after DotD!) could focus on the Black Sea region - Georgians, Armenians, Romanians and Khazars. New architecture style - Byzantine / or Black Sea for Byzantines, Bulgarians, Georgians and Armenians.
Other DLCs could be:
- Highly Developed American Civs DLC - Misippians and Muisca
- India DLC - Bengalis, Afghans, Dravidians, and Punjabians
- Asian Forgotten Empires DLC - Siamese and Tibetans
- African Powers DLC - Congolese, Zimbabweans, Somalis, Mamelukes and Kanem-Bornu
- Central European DLC - Aragonese, Venetians, Bavarians (southern Germans)
- Natives of the Americas DLC - 2 civs that would have 3 UU each and would represent to a large extent the Indians of North America, and the other civ from South America.
- Forgotten Regions DLC - Inuit and Polynesians
Unfortunately, it was very difficult for me to fit into the “50 civs limit”. That’s why I replaced as many as 32 civs. A total of 69 civs - no associations 
The symbolism of this number means that opposites attract and complement each other. So I guess it fits AoE 2.
To facilitate the selection of civs for the game, all civs could be regrouped into four subcategories - Asian civs, African civs, American civs and European civs. This way, the player would choose a region that interests him before choosing a civ to play.