This is reasonable. There are just so many areas that AoE3 hasn’t really explored.
Also agree with a South American DLC. Some good choices include:
Mapuche civ for a native civilization. Fairly popular choice. Already in AoE2.
Brazil for a relatively straightforward Federal American civ, using the various provinces as age-up options. It’s a popular choice.
Gran Colombia would be interesting way to do more revolutions and incorporate additional Latin American country independence movements (Venezuela, Equador, etc.) and plenty of separatist juntas for age up options.
Full credit to untitledjuan for this age up/revolution concept: