I can try to make 50: (I don't see why any of these shouldn't be included in this and future games)
1. America
2. Egypt

3. Rome
4. Greece
5. China
6. England
7. France
8. Germany
9. Russia
10. Babylon
11. Japan
12. India

13. Persia
14. Aztec
15. Arabia
16. Mongolia
17. Spain
18. Mali (should be staple of West Africa)

19. Ottomans
20. Inca
21. Maya
22. Korea
23. Khmer (should be staple of SE Asian)
24. Dutch
25. Portugal
26. Ethiopia (should be staple of East Africa)
27. Carthage
28. Byzantines (Not Alternate Rome)
29. Sumer (Cradle of Civilization)
30. Austria (More than just Germany 2.0)
31. Brazil (Seems to be the go to Post-Colonial SA power, and I understand)
32. Assyria (some might disagree but formed very large empire encompassing almost all Ancient-Near East)
33. Poland (Seems to be a new Staple/Maybe Sweden instead?)
34. Zulu (Have to live with it)

35. Italy (I'd like for it to be one cohesive Civ, but if not rotate the city-states in the future: Florence, Genoa, Venice, Milan)
Here's where it gets tricky:
36. Celtic nations: Ireland, Scotland, Gauls
37. Ancient Middle East: Hittites, Phoenicia, Israel?
38.

Viking: Norway, Denmark, Iceland?
39. Other South American Natives: Mapuche, Muisca, Guarani
40. West Coast of Africa: Benin, Ashanti,
41. Southern/Central Africa: Swahili, Kongo, Zimbabwe, Maputa
42. South American post colonial nations: Gran Colombia, Argentina
43. Other post colonial nations possibly: Australia, Canada, South Africa

(wouldn't have to take other slots)
44. Western NA tribe: Apache, Sioux, Navajo
45: Eastern NA tribe: Iroquois, Shawnee, Cherokee
46. SE Asia rotation: Siam, Indonesia, Vietnam, Phillipines (ideally choose more than one)
47. Central Asian Steppe: Scythia, Huns (maybe not), Parthians, Timurids?
48.Other Europe: Georgia

, Bulgaria, Hungary, Romania (no vampire emoji?), Sweden, Macedon?

(If Greece doesn't get Alexander, can be more than one in rotation due to many options)*
49. North Africa, Moors, Morocco, Nubia
50. Polynesia: Maori, Samoa, Tonga
Edited version.