I think that a civ that will appear in the game must be "unique" in terms of strategy. Is a thing that goes well while there is a limited number of civs but trying to put too many you end to make some civs much similar to each other.
You did already a good job to wich is worth and wich is not. I'll give you my opinion:
I haven't much knowledge of South America, but I think Uruguay and Bolivia are the best options.
About central Americans, I have no Idea. Do you plan a single civ that act as a whole?
You don't have much choice here, but South Africa and Ireland are the most interesting but I can see Ireland as "last option" since it's a minor nation.
For the Indians I think the developers would rework it to show the influence of the Brits, but nothing more because is already unique as it is.
Europe is already quite crammed, but I guess the Swiss and Bavaria could be an interesting choice, but, as the same for Ireland, they are minors, so I see them in a last update.
I see poland more like an European nation, but is an interesting civ nonetheless.
I don't know about the Cossacks, for what I know they are quite interesting, but they wouldn't be too similar to russians?
There is so many civs here, but is hard to figure which is actually worth to be implemented.
For now, remove the Maya. They were pratically extinct in the mod's period.
For what I know, Moroccans, Somalians, Dahomey and Benin would be interesting.
Is so complicated even there: many nations but of little worth.
I think here te focus should go to Indochina, so Burmese, Javanese and Malay are interesting choices.
Punjabis, Marathas, Mysorean and Tibetans are nice, but they are minors. Same problem as above.
Weren't Omani, Persians, Afghans and Uzbeks? Anyway, one we will see the Middle Eastern culture implemented, I would be really interested in Arabians and Armenians
I first would see what the developers take out, then we can make hypotesis. It's just too early.