[johannes1234321]

There are many, people doing (good, valuable) things on PHP, however active people with deep understanding of the engine can be counted on less than a hand. (I contributed some small things to the engine and other parts in the past)

[kingofthehill98]

One of those people is Nikita Popov (nikic). PHP core development took a hard hit when he left to work on other projects at JetBrains.