Even the bits of Philly with the most problems with vacant properties aren't actually that, well, vacant. This is a horrible racist solution which doesn't actually manage to solve any actual problems. In a truly neutron bombed urban area like, say, Flint, consolidation is perhaps a legitimate thing to consider.
Whatever problems the urban hellhole has, its dirty little secret is that its leaders needs to start thinking a bit harder about the "problem" of this new phenomenon of population growth instead of being trapped in decline thinking. At least for the moment, the era of decline is over. That could change, of course, but it's time to start thinking about how to deal with a growing population, something the city hasn't had to do in a long time.