@Jace27, even if they do that, which probably wouldn't be a bad idea, you have to consider in the end the motivation behind such a choice. They would have to ask themselves;
1) are we adding these new characters because we want to draw in more people?
2) Are we doing this as a big P.R. Stunt?
3) Or are we doing this because we want to take the world of MTG into new directions?
The country that I live in (The USA) has
gone through many cultural upheavals in its history and adding new ethnically rich characters just for the sake of having them might cause more issues than it solves. Now if they were to revisit worlds such as Arabian Nights (where that ethnic group would be prominent) THEN the change would
serve a dual purpose. Just how when they went to Tarkir and most of the natives were of an Asian Ethnicity. It tied into the environment, it was relevant to the story and the
development of MTG across the multiverse. If WOTC tried doing that then we may start to build a larger roster. Also keep in mind that becoming a planeswalker is a rare feat that only happens so many times. Its not like they can grow planeswalkers like plants.