This question was based on a combination of the base rate and the increasing number of megachurches.
In particular, 70% odds for the first such scandal to reach those who haven't heard about earlier scandals (if any) is absurd (again, unless you know about some change).
But these scandals do occur. A naive base line rate puts them at around slightly over one every two years. Prior example scandals include Ted Haggard (2006) and Eddie Long (2010). I picked a rate slightly higher than the expected from the historical base rate primarily since the number of megachurchs has been growing over the last few years. (Note also that I used a stricter definition of megachurch than is often used. 2000 regular congregants is often the dividing line, not 3000).
There's another reason to expect an increasing rate-- it's harder to keep secrets these days.
As we did last year, use this thread to make predictions for the next year and next decade, with probabilities attached when practical.
Happy New Year, Less Wrong!