A question from Brussels

When is sustainable development not enough? I'm in Brussels today for the ECTP Awards and celebration of 25th anniversary of the founding of ECTP - CEU, european of spatial planners....one project with special recognition representatives Ashok Bhalotra from the Netherlands city of the sun project urged the audience to think beyond sustainable development, likening the concept to a marriage! Would sustainable be enough for a marriage? So what's the vision? What's beyond sustainable development?