"Blond-haired Prince Charming Totally-Not-a-Scalawag John Smith leads the Powhatan in
Walt Disney's Civilization VI..."

I guess we already have Aurora leading the French/English and Maui leading the Maori, so why not?
Elsa leads the Saami. Aladdin leads the Mughals. Ariel leads Jamaica.
So this is a map created by
u/DerPhilstift on reddit. I think it's a really good representation of large cultural gaps on the map. The five "big" areas they noted that could be filled are in red:
* Western America (vaguely covering the Shoshone, Sioux, Navajo, Apache, Comanche regions, could also include the Tlingit/Salish/Haida).
* Western Africa (Morocco/Berbers)
* The Swahili Coast (Swahili/Oman)
* Burma (BURMA!!!)
* Vietnam (a bit smushed in there but we all know it's a highly requested civ)
(Other
large regions that were not highlighted include were the sub-arctic civs like Sibera/Inuit/Saami which although cool would be mechanically stretching to fit the game; the Philippines which is really hard to argue for as an "empire" and is in the Spanish city list
and would crowd out Vietnam, and Kanem-Bornu, which I think nobody disputes should be more than the city-state it already is. Also, the user forgot to fill in New Zealand for the Maori.)
For the most part I think these five regions represent the best spots for to be filled by large, influential cultures and I feel the game would feel a little less than complete if we had Canada and the Cree but no Morocco or Burma.
I'm mostly including this to illustrate that, by and large, VI has been concerned with "gap-filling." Just look how cleanly they filled out most of South America with four civs (adding a whopping two new civs to the region). They also added two new civs to North America to fill out the Canadian provinces, making a very large, clear space that wants to be filled in the Western U.S. America, aside from the Western U.S., has been pointedly "filled out" with civs and city-states.
It is looking at maps elegantly puzzle-pieced together like South America that make me look at Africa and think "why
wouldn't they give us a Morocco/Berber and Oman/Swahili civ? Just look at all that space, all that culture without representation." If the devs saw fit to go out of their way to include the
Mapuche and the
Cree where Colombia and Canada would have been accepted as "enough," just to fill out empty regions of America, why can't Africa benefit from the same philosophy? It's not like Africa poses the same development problems as Siberia; in fact one could absolutely argue that the Swahili and Berbers had even stronger infrastructure and unified identity than the Cree or Mapuche. Both were arguably the core of what later developed into the Omani and west Arabian empires. I really just don't see the
point of VI adopting the sort of design philosophy that has given us an America that looks like this without also completing Africa.
And it is especially looking at South America, so chocked full of representation with four civs and three city-states, that makes me wonder why we have only Khmer and
no city-states in mainland SE Asia. No Burma. No Vietnam. No Bangkok. Not even Kuala Lumpur or Manila. Yes, I know we have Indonesia and Bandar Brunei/Nan Madol, but I don't think anyone could argue that these are adequate substitutes for some very large, enduring, influential empires that have yet to appear in any form outside of the Path to Nirvana scenario. It really is baffling to me why this part of the map has remained so empty in a game that, with respect to nearly every other region of the world, is determined to represent every major empire and kingdom with at least a city-state.
These are two major areas that make me think that NFP couldn't possibly fill out by itself. I have a strong suspicion we will see further content after NFP if development isn't pulled completely.