Gay marriage a statistical inevitability?

Nate Silver of FiveThirtyEight.com was my favorite blogger during the election cycle, chiefly cause he was just right so much of the time. His statistical models were so on the money that I guess he decided to continue after the election, by just modeling random shit. Last week, though, he put out some data suggesting that gay marriage will be basically a done deal by 2020ish. FTA:

It turns out that you can build a very effective model by including just three
variables:1. The year in which the amendment was voted upon; 2. The percentage
of adults in 2008
Gallup tracking surveys who said that religion was an important part of
their daily lives; 3. The percentage of white evangelicals in the state.

Interesting model to me, what do y'all think?