In my opinion, the first priority is the second South American civ - to be on par with the number of American civs. In this case, the strongest candidate is Muisca civ.
Personally, I would prefer one American DLC adding 3 pre-Columbian high-developed civs:
Culture Czibcza-Muisca (Spanish. Chibcha-Muisca) - the culture of peoples living during the conquest on the Colombian highlands, east of the headwaters of the Magdalena River, in the vicinity of today’s cities of Bogota and Tunja. These peoples called themselves Muiska or Mwiskami (Muisca, Muysca or Muexca) which means “people”, “persons”, man ". They created a culture that developed from around 1000 to 1538 and is considered to be the third group of high civilizations of pre-Columbian America, but inferior to the achievements of the Maya and Aztecs in former Mexico and the Incas in the Andean highlands.
P’urhépecha created their own state in the pre-Columbian period, which was one of the most important civilizations of Mesoamerica. Its capital was Tzintzuntzan. The country was never conquered by the Aztecs despite several dangerous invasions on their part. The Tarask family was multi-ethnic. In addition to the purepecha-speaking people, there were also representatives of the Otomi, Matlatzinek, Mazahua and Nahua-speaking peoples. Presumably it was more centralized than other Mesoamerican states and empires. The Tarasks were familiar with copper and bronze metallurgy, which they used to make weapons, ornaments and everyday objects. The knowledge of this craft probably came from South America along the sea route along the west coast of the continent. The oldest copper products come from the years 800-900, and the bronze products from the years 1200-1300. Thus, unlike the Aztecs and other peoples of the pre-Columbian Mesoamerica, the Tarasks were representatives of the peoples of the Bronze Age.
Chimor (also Kingdom of Chimor or Chimú Empire) was the political grouping of the Chimú culture. The culture arose about 900 AD, succeeding the Moche culture, and was later conquered by the Inca emperor Topa Inca Yupanqui around 1470, fifty years before the arrival of the Spanish in the region. Chimor was the largest kingdom in the Late Intermediate Period, encompassing 1,000 kilometres (620 mi) of coastline. The Chimú people are best known for their distinctive monochromatic pottery and fine metal working of copper, gold, silver, bronze, and tumbaga (copper and gold). The pottery is often in the shape of a creature or has a human figure sitting or standing on a cuboid bottle. The shiny black finish of most Chimú pottery was achieved by firing the pottery at high temperatures in a closed kiln, which prevented oxygen from reacting with the clay.
After the release of such a DLC, we would have 3 for each of the Americas - a total of 6 American civs. Little but always better than just 3.
These DLCs could add a whole new architecture set: the Andean Set. The current Native American set has been renamed Mesoamerican set (Inca elements would be removed from it).