this is the other side of gentrification. as the urban poor are displaced from cities, they are not going to retreat to the rural areas with which they have no connections, they are going to remain nearby. aging suburban housing developments are available, and they will only get cheaper as the boomers die off or move into nursing homes. in the coming decades, poverty will be defined by long commutes and isolation, and the urban areas that provide short commutes and a sense of community will only be available to those who can afford the rent.
I believe it has happened to an extent here in the Detroit Metro area. However, I don't think it's the poorest that have been displaced from the city, but a lower middle class that wants out of the city, and can afford some pockets of the suburbs. Detroit, like many places, is one where income and race maps strongly, and I think this influences the perceptions people have about suburban communities as people move in and out.