Background dim seems to be a difficult topic to find consensus on. A possible solution would be to apply an additional dim, but only in a smallish radius around circles and sliders, to improve their visibility when playing with low background dim.
To make it blend in better, a gradient could be used so that the dim is darkest closest to the hitobjects.
This is something that would be difficult to implement cleanly using skins, because if hitobjects are close together the dim of the newer hitobjects would cover the older hitobjects and make them harder to see, which defeats the purpose. The dim would need to be applied on a layer that is underneath all hitobjects.
To make it blend in better, a gradient could be used so that the dim is darkest closest to the hitobjects.
This is something that would be difficult to implement cleanly using skins, because if hitobjects are close together the dim of the newer hitobjects would cover the older hitobjects and make them harder to see, which defeats the purpose. The dim would need to be applied on a layer that is underneath all hitobjects.