That's interesting, in my experience php-fpm has been very dependable even in demanding situations where we migrate over to new backends without missing a request. PHP applications can be a different story, but php-fpm provides enough knobs to restart problematic applications on demand. It's probably that last part of a PHP stack I'd want to replace.

Debugging application servers in production comes with its own set of difficulties, but I don't see how this one is worse than others. If anything, the ability to start new sockets without restarting the process is a plus.