Personally I think this is an excellent idea. If nothing else growing hardwords on unused land at least puts it to use. The fact that they are going to leave all of the streets in place means it is going to become quite strange to drive around in. When I was growing up in Vegas, before it covered the valley, aggressive developers had gone out and put in streets where "new developments" would someday be, and driving around had that weird feeling of sort of a maze race track. Hansel and Gretel probably will feel right at home :-).
I wonder who will be responsible for maintaining the streets? My guess is that will still fall on the city of Detroit (because the farm is paying taxes).
They could always let them go back to gravel roads; much cheaper to maintain, and if they're just for traversing through the hardwoods "forest", your top speed should be no more than ~20 mph.
And they might have to abandon some streets and only keep up the ones necessary to get around from property to property. We might even see some gravel roads in some places. :/
