The home builders treated the topsoil on the lot as a salable asset. You find a sprinkle of dirt under what came with the sod. The destruction of such a place is quite endothermic ... unless you throw a match.

The McMansions are a one way investment and a very poor one. Squatters, salvagers, vandalism, and fires are their lot. Shouldn't be all that long before you'll see folks moving into a title free house and the neighbors welcoming them as long as they get heat, lights, and keep the place up a bit. Eric's assessment of this is dead on.

It would all be likely to happen over a long time-scale and very informally - deteriorating suburbs, dereliction and arson, and any would-be developer could simply arrange another 'accidental' fire to get rid of the remains of houses in the areas he was interested in, then buy the land as wasteland.

I doubt that they would or could go to the expense of bringing in topsoil, just work around the houses, or maybe rake the existing topsoil a bit thinner.

In reality though, I can't see the land even being used as farmland in the States, they would just be abandoned.

The only reason agricultural land is in relatively short supply in the States is because of high meat consumption and subsidies for the ethanol scam.
The money in the scenario drawn would not allow for either, so no development of waste land would likely take place as agricultural land would not be in short supply absent these.

It's a different matter in Europe with land in much shorter supply, but then again suburbs there are less extensive.