Bert Boerland predicts: Within 3 years the acronym "CMS" won't mean "Content Management System" anymore but will be redefined to "Community Management System".
Markets are more likely to fragment than to consolidate so I think both will co-exist and inevitably overlap. That said, I agree with the notion that community software will continue to emerge and that content isn't king. And to contribute to the disorderly jumble that is the CMS acronym, may I suggest a third term: Collaboration Management System. It might be a better match.
Especially the introduction of SharePoint 2007 might have significant impact on this particular market. SharePoint 2007 adds features like forums, blogs, wikis, RSS feeds, news aggregation, surveys, issue tracking ... but also install profiles and custom content types. Clearly, Microsoft decided to play catch up. And rumor has it that the improved integration with Microsoft Office and Microsoft Outlook is jaw-dropping.
Drupal's document management functionality and integration with tools like Microsoft Office and OpenOffice is severely lacking. As it stands, Drupal is not a good SharePoint alternative, yet there is quite a bit of overlap in terms of functionality. It sure makes for an interesting situation.
I wonder what impact the introduction of SharePoint 2007 will have. What was once an important Drupal differentiator (i.e. bundling a wide variety of functionality into a single platform) will finally become commodity in 2007. Instead, seamless integration with other applications might become essential to compete? Interesting times!