I think that there is much more of a culture of admitting to things these days that would be more socially unacceptable than even back in the 90's. I also think that they are low balling it saying "Downey predicts the most likely changes between now and 2040 are that the percentage of people without a religious preference reach 25 percent. " I expect that number to be reasonably higher in the united states, it would be very interesting if it was 25% of the worlds population with out a preference in 2040.
I think there will be regions where it will be much higher (the south, bible belt, etc), but there are parts of this country where it will also be much lower (New England/the west coast). If immigration is opened up at the farm labor/blue collar end of the skill spectrum, there will likely be an up tick in religious observance in areas that might otherwise trend downward (California).
