By its nature, it doesn't need to be CPU intensive, and that's why companies are switching to it.
It runs on a single thread, which means is all those 200 Million users are being dealt with a single thread.
Where it benefits is, traditionally, by the time your website fetches the post data from the database when requested by a user, the thread waits for the data to be fetched from the database. Node shines here, simply by processing the rest of the data or other user queries and when data fetch is complete it gets back to it to process it further.
The thing is CPU is extremely fast. It loves revving up. Why make it wait?
Yes, PHP is one of the most popular back-end scripting languages, and that is why it is still being supported. Facebook is also adding years to PHP's life.
I am not saying you to leave PHP... you'll eventually if Wordpress will make a switch () but wondering how fast the websites will be when this will happen. You'll get the 10x speed with 1/10 of resources and fewer prices.