While the process of changing zoning can be slow and difficult, there is still time in de Blasio’s tenure to pass a plan to end exclusionary zoning. That plan could allow for the development of duplexes, triplexes or small apartment houses. It could broadly legalize “accessory dwelling units,” and set out rules for the creation of safe, regulated basement apartments. And it could revise other laws, like minimum lot sizes and parking regulations, that prevent the creation of new, affordable housing.