The idea its a man made Biome as a consequence of using too many polluting machines (The more machines of these kind you use, the more pollution), pollution can be avoided by not building too many of these or simply placing these far away from your main base. Kinda like the Taint its working in thaumcraft, too much and it becomes a shithole, too little and you barely notice it.
i'm think what the implications would be for smp what if your neighbor doesn't give a crap about his pollution cause he is a rich donater and can teleport to his beautiful jungle retreat while he pumps his sewage into you back yard