It is difficult to imagine that the urban underclass would ever be pulled (or pushed) to the suburban fringe, due to the disadvantages of increasing energy costs and general lack of transportation infrastructure. Unless some begin to form "kitchen suburbs" and grow food out on the "Crabgrass Frontier" just to survive in some apocalyptic scenario, cheaper housing prices would not be sufficient enticement.
Small towns, too (about which there is little research) have experienced a type of suburbanization--in addition to the ex-urban spatial invasion by cities--in which tract subdivisions lying close-in have aided in obliterating downtowns in an empty-center doughnut effect. Instrumental in this, of course, was WalMartization--the big-box competition which boarded up mom-and-pop America--occurring as residents with the means to do so moved out to the edges. I speak from personal experience, when I say that small towns have, also, lost their walkability.
As in larger urban areas, housing stock in many small-town neighborhoods have become dilapidated. I was shocked to see that middle-class neighborhoods where I used to play in my small hometown in Kentucky have morphed into white ghettos.