I think Captain Kwok is already doing this in Space Food Empires, but I had an idea for how to implement pollution in a mod, even though SE4 doesn't allow facilities to degrade a planet's conditions!
1. All polluting facilities should cause populations to grow unhappy in addition to "degrading" the conditions of a planet.
2. The pollution control facilities should cause populations to grow happier, as well as improving conditions.
This way, if you have more pollutants than pollution control, the conditions won't degrade, but at least the population will grow unhappy. Of course, if you have too MUCH pollution control, the planet will grow unusually happy in addition to its conditions improving...
But that can be worked around by making pollution control facilities much more expensive than happiness facilities or climate control facilities...
Pollution Workaround
Threaded Mode