If you're like Facebook and started out with PHP, built your own compiler for it, and have a brilliant engineering team that regularly comes out with products like Haystack or Cassandra, then go ahead use PHP.

But you're not Facebook are you? You're not the go-to source for graduates in the top of their class. You're seeing incredible traffic, and the original source is not a wet pile of spaghetti mushing up every improvement you try to make.

Perhaps then its fair to say you shouldn't have used PHP, and instead used a language that was a better fit for your organizations structure and practices at scale.