In another thread, Will Johnson (I think) argued that activity levels (new articles, in particular) would continue to decline rapidly in the next few years and that by Christmas we would have fewer than 1000 new articles per day. Looking at the new stats, I'm more confident that en-wiki can maintain a steady state of activity something close to the present level (especially as the usability efforts begin to make it easier for newbies to edit, after years of increasingly complex markup that did the opposite).
Perhaps rather than counting new articles, we should be looking at the amount of text added to articles? As I understand it, there's a bit of a shift going on from creating new articles to improving existing ones, and that seems like a reasonable metric to measure that from (especially if only article text, rather than templates, was counted). Of course, it's also a lot harder to calculate...
Mike