I think if the states really wanted to get the EPA to not enforce CO2 emmisions as pollution, they should try to get the Clean Air Act amended rather than waste time sueing the EPA (which is not likely to have any actual effect, they are bound by a decision of the Supreme Court to regulate CO2 as pollution).
The optics of this look better for state AG's and Governors however as it casts them in a light of "standing up to big government", really I think it makes them look foolish as there are better ways they could approach this problem. Maybe I'm wrong though, YOMV.
Are you saying that a court has told EPA that they can't change the regulatory threshold for CO2 from 250 tons to 25,000 tons(or maybe 70,000 tons)?
They will get sued for such action, but I wasn't aware that a court had said they couldn't try.