That will literally never happen. If anyone seriously believes that there will be a day without the legal ability to purchase some media or to publish media without making it DRM-encumbered has some serious issues with their thought process.

Has there been any point in history where it has been easier to make a movie, record a song, or write a story? Has there been any point in history where our culture has been more free? Man it would be a shame if we didn't get to see the latest Hollywood blockbuster, but culture will always continue. There's no way to remove that right within any legal framework.

It doesn't need to happen within a legal framework, it will happen within a technical and social one. Mobile platforms are walled gardens, that deliver DRM-crippled content. When the ability to sideload media content is quietly removed from the next version of your favorite mobile OS, how will you get your DRM-free content then?

As long as you can publish on the web, as long as you can write an email, as long as you can make a phone call, send a text, or even talk to the person standing next to you, culture still goes on. There's literally no way to stop it without the death of mankind.

What you're worried about is that we won't be able to buy a copy of the next superhero movie. Oh well. There's still plenty of free and worthwhile works of media that can never be forced to close.