One point I've been meaning to make and haven't seen mentioned is that the Chinese and especially the Indians have said their per-capita emissions won't exceed the US or the industrialized world average, respectively. If we reduce our emissions, that tightens the level that they've promised not to exceed.
I think this is worth submitting as a comment on the proposed EPA regulations. Unfortunately it's not an airtight argument because the promises aren't airtight. The Chinese commitment was by a high-level government official, not a legal pronouncement (and not entirely clear that the bar adjusts downwards as US emissions decrease). The Indian commitment was by the then-Prime Minister, again helpful but not binding. The Indian statement also included a confusing disclaimer that limiting US emissions was necessary but not something imposing requirements on India as well. I think the way to resolve the confusion is to assume it meant that the US emissions needed to drop while Indian's very low per capita emissions needed to grow, but grow only up to a certain point.
One diplomatic goal should be to make these commitments binding and to obtain them from other countries. The other point is that they're not enough - if India ever neared current industrialized world per capita emissions, that would be the real game over for the planet. We in the West have to realize we're asking far more of the developed countries than of ourselves.
In the long run, post 2050, developing world per capita emissions should actually be higher than the developed world. Best case scenario is the developed world has sharply negative emissions and developing world has modestly negative emissions. That might make up for some of the inequity in prior carbon emissions.