Really quickly: the fact that diversity is contextual is what makes it diversity. If one set of adaptations in evolution were always the right one, there'd be no such thing as biodiversity -- there would be a homogenous population of creatures that all had stumbled their way towards the same set of adaptation. Evolution is driven not genetically, but by the environments creatures find them in.
That's why the New York centrism is part of the diversity problem. If we have a system in which there's only one environment where theater can thrive at all, then we're not going to have a lot of diversity.
In fact, one thing that might help diversity would be to have diverse methods of production and distribution. A multiplicity of contexts in a multiplicity of communities will be far more likely to produce diversity than trying to find a way to get a diverse number of people to apply for the same ten not-for-profit theaters in New York City.