There are 32 bulletin boards listed in the Wikipedia article Comparison of Internet forum software (PHP). Only ten of them have had any kind of a release in 2011 so far. Of those ten, only XenForo and BeehiveForum have made feature releases this year.

To me, this is evidence that the products are mature. As "revolutionary" as XenForo was supposed to be, it seems to be running less than a thousand sites. The other commercial developers have made sure to copy the unique features for their upcoming releases (IPB 3.2 and vBulletin 4.1). But even though the effects of competition are meaning new features, I don't see many users clamoring for those features. Some, sure, but not even a major fraction.

Does the relative stagnation mean the products will slowly disappear? I suspect that many of the smaller free solutions will go away. The same for many of the smaller paid solutions. This is more of an effect of fewer individuals starting up their own sites to satisfy their egos.