Detroit already has a plan that involves voluntary relocation. Essentially, city-owned property in stabler neighborhoods will be offered to residents of primarily empty neighborhoods. Services will then be cut in the emptier neighborhoods, allowing the city to better focus on the stabler neighborhoods.
As far as demolition. It generally costs as much as $10,000 for the city to demolish a vacant home. There are plans to stream-line the process, hopefully reducing the cost to as little as $2,500 per house by among other things, offsetting the cost by stripping and selling valuable materials. Even then, the city doesn't have all that much money it can dedicate to demolition. The current administration has done a fairly decent job of demolishing, upwards of 10,000 derelict homes and buildings, but that's just scratching the surface. It would be interesting to see if the city can declare a state of emergency, allowing for more federal funds to help demolish derelict homes, but it certainly wouldn't happen under a divided Congress.
In any case, Detroit does have a framework in place in how it can grow and stabilize the better parts of the city and deal with the worst parts of the city.
http://detroitworksproject.com/the-framework/