We continuously bring up the city-nature dyad only to lament the exclusion of a third term. Practically anything can be framed as the excluded third of a dialectic pair. This is how post-Enlightenment thought works. Sanford Kwinter, in his opening address to the keynote, argued that what is excluded by the "false dichotomy" of technology and nature is nothing less than the "social and cultural dimension" itself. I would argue, to the contrary, that ecology is typically approached today as a matter of existential praxis - even by those technocrats and hippies that in the end address ecological problems within the narrow means of the technology-nature dyad. The problem is one of feasibility: a technological or naturalist scope each yield results that are implementable in our liberal/capitalist world, while an "existential ecology" yields unbuilt utopia. I would argue that the blind spot Sanford points out does not in fact exist; scratch a technocratic or hippie environmentalist and you will find the sensibility of a deep ecologist.
Rem Koolhaas thankfully presented a resolutely hybrid interpretation of ecology. His argument incorporated a narrative of "reasonable progress" and a narrative of "disasters," each of which contained a social/cultural dimension. Rem's excluded third was the pairing of knowledge with ambition: he lamented the "devastating effect on knowledge" of ways of working with informal architecture that occurred during the growth of the market economy post-1970. The ways of quantifying ecology developed during the 60s were not advanced beyond a touchingly naive stage. The ambition to carry out large scale projects with serious ecological impact - exemplified by Buckminster Fuller - imploded during the same period.
Both Sanford and Rem argued in a way that carved out a niche for themselves, one as a practitioner of the formal where it intersects with the informal, the other as a theorist working on the specific social and cultural dimensions of the science of ecology.
Homi Bhabha spoke with greater disinterest and less directness; I will need to look over his argument once again before I begin to understand it.