This is a really interesting discussion with some great commentary.

From my perspective, it would simply take arrogance for WordPress to loose its standing. The kind of arrogance where WordPress no longer listened to the needs of its community or lost it's current vision. The kind of arrogance that a lot of corporations are consistently guilty of (they never learn), driven by greed and a loss of direction away from the initial core values that helped them grow in the first place.

So, far, WordPress has successfully adapted more towards a CMS and application framework because people (developers, designers and end users) have needed that functionality. Combine this with WP being steered towards that overall utopian goal of making content management as simple as possible and you have a CMS that can be picked up and easily used (relatively speaking) by its main user groups. Take the antithesis of this (Drupal) for example, for a long time (prior to version 7) it largely ignored the concerns of the design community and end users as it pandered almost exclusively to developers, yet, because of that it became difficult to use for anyone but the most technically minded. It's that vision and perspective from different sides of the equation that WordPress currently has and other projects still lack.

Okay, WP is not perfect at anything - whether that be blogging, more traditional CMS functionality or an application framework - and the argument about it becoming bloated is already a very real concern. Though, I'm sure over time this situation will improve as certain issues become more apparent and as long as community concerns are met. That overriding philosophy that WordPress has of 'democratising the web' simply cannot be met without meeting the needs of developers, designers and crucially the end user.

As long as WP continues to pay the utmost respect its community, I think it will continue to thrive. However, the minute that WP loses perspective and ceases to adapt and move towards a genuine greater good is the time that it WILL fail as so many have before.