What if you set up a Dead Man's Switch of sorts, that you were unable to disable, that would go off and notify a trusted journalist/blogger/etc if you ever tripped it? Tripping it would happen as a result of whatever rules you put in place that make it overwhelmingly likely you're snooping around in your user's data.

The logistics behind this might be hard to pull off. I really don't know enough to know whether something like this is feasible, but if the concept was feasible to implement, it seems like you can just publicly announce ahead of time that the system is in place, and it's out of your hands.