Nate Cohn thinks it will be a long, long time. Andrew Sullivan reports at the Dish:
With evangelicals slower to change their minds, Southern states should move at a slower pace than the national average. To date, support for gay marriage has increased at a roughly linear rate of 2 points per year. But it’s possible that increases in support could slow in the medium-term, as non-evangelical groups hit the point of diminishing returns. If evangelicals don’t pick up the slack by shifting faster on gay marriage, support for gay marriage could plateau. Parts of the South, Plains, and West would probably still have gay marriage bans, and the Supreme Court, despite its hopes to avoid a judgment, might be forced to make the final call.
Not holding our breath.