In a new post to his blog Marco Tabini poses an interesting question - is PHP running out of itches to scratch in the evolution of the language?
think it's fair to say that the pace at which PHP core is being developed has slowed down considerably over the past couple of years, while the development of many projects based on it, like programming and application frameworks, has sped up and continues to grow at a fast pace. But this doesn't mean that we're running out of steam. The PHP ecosystem is simply refocusing outside of core, where it has a lot more freedom of action.
He suggests two reasons as to why this slowdown might be happening - first that there's not a sense of strong leadership in the core development group (a feature of the project done on purpose) and the change to move new library support out to PECL and PEAR instead of directly into the core of the language.
The risk facing us, as I see it, is not that Drupal, or WordPress, or whoever may decide to fork PHP or abandon it altogether. Rather, the problem is that there is no real way for these projects to provide upstream positive feedback to PHP core.