The only way that will ever happen is if the moralist fascists vying for power in conservative parties win, because getting rid of porn is going to piss off a lot of people.

Popular attitudes will eventually swing to favor piety and austerity. Likely accelerated by material decline which historically has changed social behavior. When the elderly, possibly seen as contributing to the next generations’ problems, are complaining about young people not making enough porn, not many will be quick to oblige them. Change in moral standards doesn’t require legislation or revolution.

There will probably be less porn in 50 years than now just because moral fashions change, and it would be difficult for there to be more of it. I see the challenge to it coming more from the left than from the right, though.

It's a bit like a minimum entropy point :)