Number of available developers is still high but it could be even higher if it had the same successful propaganda as JavaScript or Python.
There is nothing in the language itself that should stop it from competing with any general purpose language, not anymore.
I think this is the next important step for PHP, have charismatic & humorous evangelist like Douglas Crockford.
Crockford’s missionary work was done during a time when JavaScript was in a big expansion because everyone wanted to write single page applications.
But today there is huge JavaScript fatigue and more and more developers have start to realize that server side rendering is (back to) the future for most of the traditional web, especially in a time where time to market has become even more important.
The constant churn of the JavaScript realm have now reached epidemic levels, a massive & relentless wave of deprecated and unsupported projects sweeps over every organization. Somewhere right now some poor developer inherits a Angular 1.1 project built with gulp.
I think also there have been a shift in regards to fullstack developers versus frontend & backend developers, many companies have woken up to disastrous idea of splitting frontend & backend developers into separate teams and now merging them again, as result the fullstack developer becomes more important. PHP is in my opinion best fullstack web platform you can use.
Say after me, No more build steps for rendering a paragraph, no more unhandled Ajax errors, no more REST JSON apis with only the frontend as consumer, no more reimplementing the database schema in JavaScript, no more asynchronous state rendering on the same page. <Insert Braveheart meme>