Good grief. When the power goes off city wide, at least the metropolitan residents of today can potentially experience that rare moment of gazing up at the sky like
limp-brained turkeys and being awed or frightened by a tapestry of strange, glowing dots in the sky. Future generations bred under this orbiting sky-mirror trend may output a percentage of the population that is lifetime barred from such a sublime revelation (i.e., the timid non-nomadic ones who never venture out of city limits to risk those horrors lurking in the feral and barbaric outlands).
Ralph Waldo Emerson: "
If the stars should appear one night in a thousand years, how would men believe and adore, and preserve for many generations the remembrance of the city of God which had been shown! "
~
On the one hand is light pollution and the effects of light on the pineal gland through the increased chances of sleep deprivation and lowering melatonin production. There is also the concern that the solar energy reflected would have otherwise been lost, by putting it into our ecosystem it will further increase global warming and extreme weather patterns. (diffusion could probably help reduce that)
On the other hand if it was used to extend daylight hours (as opposed to lighting up the whole night) it could reduce accidents, lower depression and reduce the costs of street lighting.
furthermore there is the potential of weaponisation. For instance if you have thirty+ satellites in geosynchronous orbit, it could be possible to tilt all the solar panels on them to reflect sunlight at a given point on the earth's surface, subsequently cooking what ever happens to be focalised at the point of intersection.
The skeptic in me makes me doubtful that this will ever happen. It's a Chinese city (Chengdu) that's proposing this, not their national government, so it might turn out to be a pipedream boondoggle. (Was it that new Canadian cannabis in Chendu's pipes?)
There's no way that these reflectors will be as big and far away as the Moon, they will be far smaller and closer. Putting them in geosynchronous orbit makes the most sense so that they will always be above and directed at Chendu. But that suggests that they might not be light-polluting our North American or European skies, so maybe our astronomers will be ok.
But putting these things above China might not be good for Chinese astronomy.