Brief answer:
The present economic level is already unsustainable for future survival. Sustainability is not mean to be kept going and not collapse immediately while drag along as far as it can until it cannot. Sustainability is the rational open process that can connect the closed natural process and bridge us into endless future.
Therefore, the only sustainable development for this economy is the rational order directed manmade and planned negative development.
More explanation:
Fundamentally, we have to adapt the nature given conditions to survive into future, because fundamentally, intelligent life cannot manipulate the nature to get our way ahead wilfully and subjectively. That is because:
We cannot reverse entropy growing process to create material value in this local space and time.
We cannot influence the natural evolution and distribution of material value in local space and time.
We cannot survive and travel in space to access the material value in other local space and time at our present level of existence (unless we can evolve in our nature given conditions for the next giga years to reach that evolution distance to realise that evolution level).
The only thing we can depend on to access future is the evolution level that enable us the fundamentally different existence state to survive that fundamentally different environment conditions of the future while that evolution level is defined by the evolution distance, and this evolution distance is supported by the material value as its material base. But our present way of production and consumption is irreversibly consuming/destroying it that is shortfalling it that will cut short our evolution time to extinct us.
We are locked in this self-destruction process because the natural order is running this social system.
Conclusion:
Therefore the most important thing for sustainability is the change to rational order for our social system.
