Coordination is surely an issue. No one wants to make the first move because it's so risky. But surely the goal is dense, vibrant, dynamic neighborhoods. Being the first to move into a neighborhood or city that's blighted or vacant means a several year to lifelong commitment. That's a huge investment for an unassured thing. But one would have to conclude that it's absolutely necessary. That's why I light up at new experiments like these. Create some data. Start a discussion. Unfortunately, I know nothing about city building codes and what stands in the way as especially onerous regulation, so I can't speak to your point about construction in the 80s. That does sound like just a convenient cutoff point--as far back as we can go before we start insulating with asbestos. The 1980s don't strike me as an especially innovative time RE construction, but again, not my area of expertise.