America
As for South America, it needs at least two brand new civs - to be aligned with South America. Due to the fact that North America has 1 highly developed civ (Aztecs) and two indigenous civs (Lakota and Iroquois), I think that South America with only Inca (highly developed civ) should receive two new indigenous civs - Mapuche and Tupi. It would be a South American DLC.
Potentially, there may also be highly developed American civs DLC from Muisca and Maya civs in the future. Then we would have 8 native American civs (4 from North America and 4 from South America).
More maps with the new Minor Nations for South America are necessary. North America could also get some news. An American Minor Nations makeover could also be.
The USA civ opened the way for America’s most powerful revolutions - it wasn’t necessary, but it has already happened. It is a pity that the US civ did not add the Mexican civ as well, as it would be an equal continental rival. The Brazilians and Gran Colombians (and possibly the Argentines as well) are also worth adding for the USA civ in the game.
Asia
The first thing that comes to my mind about Asia is a weak Minor Nations. I would prefer that, like other continents, Asian maps contain Minor Nations - not Shaolin and Jesuits. Asian maps should receive more Minor Nations based on Asian nations such as Afghans, Tibetans and Koreans. You could also add some maps from Oceania that include Minor Nations such as Māori and Aborigines. The current Asian Minor Nations could be present on the maps simultaneously with the new Minor Nations (mixed). On some current maps, the current Minor Nations would be replaced with new ones for greater accuracy and correctness.
Of course, this game lacks such Asian empires as the Persians, Siamese and Omani (or Arabs) - these are undeniable candidates for new civs. Potentially, 2 other civs could also be added - Vijayanagara (South Indian Hindu Empire) and Tatar-Mongolian civ (nomadic civ representing North and Central Asia).
Africa
MORE MINOR NATIONS PLEASE 
There is a new civ on the horizon and most likely it is Moroccan civ - all indications are that; it will probably be added for owners of African Royals DLC.
In the future I would like to see more African civs such as Congolese and Mutapa.
South Africa maps with Minor Nations are sorely lacking. Maybe they will be added in future updates or maybe in the South African DLC (with new civs)?
Europe
Finally, I left Europe without maps and Minor Nations. Of course, it is logical that if they only appear in the paid DLC, just like the African maps.
The European DLC could be a relatively large DLC modeled on the old DLC to the classic AoE 3. It could give new features and mechanics for European civs e.g. more extensive tactics for military units - new formations, attack priority (buildings or units) positioning priority (who is on the front line - infantry or cavalry?), Mercenaries would not fill the default population (Outposts would provide a special population for Mercenaries) and more animals to train in the Livestock Pen (cows, pigs and maybe even poultry: chickens and geese).
A European DLC could also add non-colonial European powers as new civs such as:
- Austria-Hungary civ
- Poland-Lithuania civ
- Prussians civ
- potentially to this group of civs would be transferred Germans civ which would become Holy Roman Empire civ
- Italians civ could also belong to this group of civs (I think they fit more here than in the group of colonial powers)
This would give us a sizeable new set of European civs that could have different mechanics and would work differently from their continental rivals who created the colonial empires.
If you are interested in what the European DLC and the new group of European civs could look like, I invite you to my topic 