> Based off of my first ever forays into node performance analysis last year, JSON.stringify was one of the biggest impediments to just about everything around performant node services

Just so. It is, or at least can be, the plurality of the sequential part of any Amdahl's Law calculation for Nodejs.

I'm curious if any of the 'side effect free' commentary in this post is about moving parts of the JSON calculation off of the event loop. That would certainly be very interesting if true.

However for concurrency reasons I suspect it could never be fully off. The best you could likely do is have multiple threads converting the object while the event loop remains blocked. Not entirely unlike concurrent marking in the JVM.