Massachusetts vs EPA environmental law and policy help?

As a result of the Massachusetts vs EPA decision, The EPA has begun to regulate carbon dioxide as a pollutant under the Clean Air Act. Representative John Digell has complained that addressing climate change through the CAA would be “a glorious mess.” Why might this be the case? More specifically, what are the potential challenges to creating a NAAQS for carbon dioxide? What about setting NSPS for carbon dioxide?

The CAA does not allow to consider cost when establishing NAAQS. Does this make sense to you? Do you think the small number of NAAQS established since the CAA was passed in 1970 suggests that EPA really does take cost and technical feasibility into account?