I think, they should stick to what they have, but add more pollution. I think a shroud of visible air pollution would be good at ground level, it would give a nice contrast when you ascend to the tallest buildings, which would be the wealthiest and most sterile locations in the city.
I believe air pollution can also distort the visible light spectrum at sunset? Creating a kind of orange glow before nightfall which would be cool.. but I'm not certain about that.
This kind of system could interplay with both the wheather and day/night cycles to create interesting dynamic combinations. Perhaps even some scenarios that reduce the pollution (after a storm..?). I also like idea of having not just trash lying around on the streets, but textures that are stained by pollution and acid rain. A lot of very off coloured concrete and rusty metal would be good. The city definately needs to feel like its struggling to maintain itself on many levels.
Those shots from BR2049 and GITS are cool but, they don't really demonstrate exactly what I'm talking about. I think this could be new territory for the genre.