I believe that the growth of PHP depends increasingly on applications like Drupal, Joomla!, WordPress, phpBB, Typo3, ezPublish and similar systems. Specifically, I believe that most organizations adopt PHP primarily because they want to use one of these popular applications which have PHP at their core. Fewer organizations adopt PHP because they want to build from scratch their own PHP applications. Hence, more than ever, the future of PHP depends on popular PHP applications that have emerged over recent years.
Conversely, the future of Drupal depends on PHP. Moreover, many of us are staking our future, and that of our businesses, on Drupal and, by extension, on PHP. The same is true for those who make their living with Joomla!, WordPress, phpBB, vBulletin, Typo3, and ezPublish.
It seems that we have arrived at a point in which there is a symbiotic relationship between PHP and the most popular PHP applications. A relationship that did not exist when PHP was created. Symbiotic relationships are obligatory: we depend entirely on each other for survival. And yet, I feel like we've been living apart. It makes sense for us (i.e, application developers) to contribute to the development of PHP, and for the PHP core developers to work more closely with the developers of the most popular PHP applications.
Having spent ten years of my life developing Java Virtual Machines and run-time systems, I feel that I'd be able to contribute to PHP. Unfortunately, I don't currently have time for it. Maybe when Acquia is a bit larger, we'll hire a full-time engineer to contribute to PHP's development. Maybe other organizations will consider doing the same, or more people will find the time to be active in more than just one project. It seems as though our future would really benefit from such people.
If you could contribute to PHP core, what would you change?