The best thing would probably be a Forgotten/The Conquerors approach if they every plan to add new civs.
Take a DLC featuring Iroquois, Kongolese, Mapuche, Siamese and Tamils and you would have a great expansion. Only issue is that it might require 2 or more different new architecture sets but with a price tag similar to the previous DLC and the value of AOE2:DE overall it would be fair I guess. They’ve basically made three new architecture sets for it.
Not in the Middle Ages, which is where AoE2 goes to.
The best chance for Cherokee, would be on an Iroquois umbrella.
If I had to choose 4 North-Am civs, I would go with:
-Mississipians (Defensive and Gunpowder civ)
-Iroquois (Infantry and Monk civ)
-Tarascans (American Cavalry civ)
-Pueblo (Defensive and Economic civ)
Though, to be honest, I would just go with 3 civs for North-Am, just like we have 3 for Meso and South-Am.