[andrewmg]

I don't think your second point is correct. Congress could most certainly empower EPA to administer a cap-and-trade scheme or even some kind of phase-out, as it did with (respectively) acid-rain precursors and CFCs. Congress could do the same for GHG emissions, without spelling out the impact on each and every affected industry or source. Congress might, for example, set an economy-wide emissions cap, set a schedule of annual caps or a formula, specify how EPA should go about determining the cap each year, or some combination of those things. If Congress specifies that all sources economy-wide (or some subset of them) will be subject to a cap, then it has answered the major question.

On your third point, see the paragraph on page 38 of my brief linked above. "Generation-shifting," as used in the CPP, was EPA's claim that it could set "achievable" emissions standards based on turning off a source. One can argue about whether new-source standards satisfy the statutory test (BACT) applicable to major industrial facilities and whether the agency's decision to set those standards at a particular level is supported by the evidence or otherwise arbitrary and capricious. But that's an entirely different inquiry from whether Congress empowered EPA to switch off more or less every source of emissions in the country as it so chooses.