I feel that Maxis are doing a pretty good job already, they have updated several black hairs and added skintones, they consult with different groups when adding content like they did with the Hispanic Heritage Month. There is always more that can be done but that can be said about pretty much everything in the game...I think a lot of reasons why they can't do more is budget and time honestly. I would have liked to see them do much more with Snowy Escape for example...
I agree that there are cultures left that could be done like the ones you listed, hopefully we will see them in future packs, the courtyard oasis kit reminded me that we don't really have a world that suits builds like that (apart from maybe Oasis Springs).
There have been other threads here on the forum about adding disability, I think a lot of people are not sure if they really want that in the game, I'm not sure myself if I want it. It's a rather hot topic so I don't wish to derail the thread.