I remember reading about some framework which was doing something nutty like embedding actual data in the comments on a function, and then parsing out those comments at run-time. For what it's worth, I believe it was on HN and in relation to the caveats for older V8 optimization w.r.t. function length (https://top.fse.guru/nodejs-a-quick-optimization-advice-7353...), but it was years ago so, as you say, hopefully they moved to something less insane in the intervening time.

Aside since you're here. The "Would it be possible to write a tool to convert serialized AST back to JS?" portion of the FAQ (https://github.com/syg/ecmascript-binary-ast#faq) says that it would be possible to generate source which would be "semantically equivalent" -- you might want to call out the Function.prototype.toString exception explicitly there, though admittedly that level of pedantry might be more obscuring than enlightening.