But I suspect it goes back rather longer. Those of us with a traditional media background always knew it was the content people bought our stuff for, for example.
Then there was the build - that not Content, but Conversation is King. Cory Doctorow memorably put it that "Conversation is King... Content is just something to talk about."
Content is pointless without conversation. Conversation needs 'something to talk about'.
Neither is king. It's the interaction of people and ideas that drives us to action. The web has lowered the barrier for millions to interact with ideas.
And no one is describing what they are interacting with as 'content'. In fact 'content' has some rather unhelpful connotations in the context of what the web is best at enabling - ie adhoc self-forming groups of purpose.
Content implies constraint; An idea boxed and kept within - a thing inside with limitations.
This isn't how people behave with ideas. We take, shape, add, delete, remodel - hack ideas in our every interaction. And the web is a splendid evolutionary environment for them.
So I'm going to suggest Concepts Are King is a better 'catch-all' for what is really important in connecting folk. I can take your boxed up piece of content and share it, of course. That's old-style viral. Pass it on unmolestered. Don't expect evolution.
Or I can connect with and play with a concept. We can.
And in so doing we add value - not mere distribution.
Image attribution: By Enoch Lau (Own work (photo)) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC-BY-SA-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/2.5-2.0-1.0)], via Wikimedia Commons