Also wasn't Slack in beginning written in PHP? The most not-realtime web stack there is. Maybe you don't have to go all in and can keep the boring application logic parts in Ruby/PHP/Python and offload the realtime performance stuff to more performant system (that can be even be in Ruby/PHP/Python because all of them offer some sort of async addon nowdays). It's strange in world where everybody is talking about microservices to be so afraid to use multiple connect tools that make specific parts easy. Like "Go all microservices but all of them in Node or Go".