PHP made a lot of mistakes. A lot. Many are still in the language today. However PHP is 21 years old now and PHP7 was released a few months ago. PHP7 is a huge improvement over old versions. If you haven't looked at it, do so. PHP sucks in 2016 is mostly FUD now.
Node JS on the other hand is very young ecosytem and it's basically repeating the same mistakes PHP did. Swarms of well intentioned, very new devs are "contributing" and it's leading to the same mess PHP was in.
It sucks to maintain a legacy mess, but the developer in question is pretty much guaranteed to be building someone's next mess if he goes with such a rewrite.
My two cents.