Like many stories, there will always be a main character and supporting characters. Even if it's split into chapters based around a certain protagnist, there will always be one that seems to play the most important role. R* have more than likely decided to give us the role of the supporting characters to play as also. In GTA IV DLC's you played as supporting characters in the IV plot.
Watching the trailer, it's clear that the narrator is the main character, and the other guys seen are supporting characters we may get to play as...
I don't see any problems playing as a white middle aged american guy... or an Hispanic guy, or a black guy. They're characters, which will have characteristics and stories to tell. It's not like they're real people leading boring American normal lives.