I think it's currently technically feasible on top-of-the-line phones to implement real time nudity detection and hiding by default. I can see it being a solved problem in 5 years. Maybe it will display at first but be blacked out after a few milliseconds.

I sure hope this blocking thing is opt-in ;-). How will adu.. ahem .. entertainment websites live otherwise ?

I imagine it will be like SafeSearch on google and bing, where it's opt-out.