When I got to the end of the article, I discovered that the researcher behind the work being discussed, Ed Chi of PARC, had a similar thought.
"In my experience, the only thing we've seen these growth patterns [in] before is in population growth studies – where there's some sort of resource constraint that results in this model." The site, he suggests, is becoming like a community where resources have started to run out. "As you run out of food, people start competing for that food, and that results in a slowdown in population growth and means that the stronger, more well-adapted part of the population starts to have more power."
But the article also says that the slowdown is caused by a shift in power towards 'deletionist' editors - it's getting harder to get stuff onto Wikipedia. Which suggests that the correct model might not be a sort of density-dependent, resource-limited population (we're running out of stuff to create wikipedia entries about), but perhaps something more top-down, like a predator-prey system (the editor population is keeping the contributor population in check).
I've no idea, but it's a question entirely suitable to the tools of ecological analysis. Someone should get onto it.
