The short version: PHP will remain popular but its growth will slow, as people get nervous about its maintainability and security stories.

He does mention the two different stances of this statement - the good side (with low entry level, good applications and speed) and the stance he seems to believe in more - that there are just things about PHP and how its handled that could cause major issues down the line.

Be sure to check out the comments for community views on both sides of the story too.