I really love your type of government. That would be great.
The different government-cities, I think we agree on that, will then not live in a concurrence between each other but in a global, lawless, human agreement ergo a non-competitive society. Because if people start to think competitive, this will have no upper boundary - that means that it would go over to a global war of competition, which once again destroys the harmony. The capitalistic, competitive philosophy therefore cannot be applied to this system you propose, as this would result in a striving for being the strongest city, taking over others, manipulating,..., therefore there needs to be a balance between these cities.
What does that mean? As the government is then made by its people, the balance must come from the people themselves. Therefore, the people must make a mind-revolution, away from competitive thinking to "social" thinking - say - replacing the ego with the others OR, to formulate it differently, they must agree, that each person is equal ergo each city is equal and no one is better or worse. Do you see any other solutions? Maybe there are.
Whatever, to come back to your question of environment, I think with the people that understand their boundaries, the non-competitive thinking, they will also be able to set limits in technology that is needed instead of how it is today and will therefore not exploit nature at all costs. It may be dreaming, but people that are in balance with themselves and society will also be at balance with nature.
I surely see the problematics in this proposed image of humanity...progress will cease of course or rather progress of technology. I don't think that this system would cease all progress - for example art is not made out of competition, neither is philosophy or, say, the formation of the human mind. I don't believe in social darwinism.