Brandsdale
Big Yella
we already learned about wakanda and their customs from the 1st filmIt has to be damn near 3 hours, and that could still be not enough. Wakanda will probably have little time and most of the film will be Shuri's global adventures intertwined with Atlantis being established.
2nd would prob just showcase other parts of the city and more cultural traditions (similar to ms marvel)
the story can still be about the wakandans and the Atlanteans but cause they are both lost cities that hide from western world and are rich in cultural tradtions, heritage, etc. so a longer movie is the only way to tell the story about these two cities and make it make sense