Hey Nemo,
That's cool that you had that discussion. I didn't know about it. As you can imagine, I've talked a lot of people about the work myself. I'm stoked that we're having another discussion right now. :)
I'm going to go into scientist-defending-the-value-of-my-work mode for a couple of paragraphs.
Our model did suggest that it is getting more difficult for *all editors* to change policies over time regardless of experience level[1]. It also suggests that this effect is much stronger for new editiors. I agree that new policy != adaptation. That's why we modeled change over time for our hypothesis test. The norm growth graph I referenced is intended to serve as a descriptive visualization.
It's important to understand that neither of these sets of numbers alone do not tell the whole story here. Quantitative hypothesis test are narrow windows through which to view the world, yet such tests are used to support or refute complex arguments. Our argument about the nature of English Wikipedia's decline was built up from current theory and our own qualitative work. FWIW, more recent research has confirmed some of our basic assumptions(e.g. [2], [3]) and I've re-measured similar phenomena with new metrics several times in the last 3 years.
An easy counterexample would be finding at least one wiki showing a different pattern in policymaking but equal patterns in everything else.
I'm not sure what you mean by "easy", but I look forward to reading your report. Seriously though, if you want to work on this, I've got some ideas and I'd be happy to collaborate.