node-fibers is one attempt to put coroutines into node. I like it because it uses libcoro, which is nice and tight and uses ucontext, and because it works as a module without forking the core of node. Once you've 'fiberized' the server modules to start each request in its own fiber and implemented a call-with-current-continuation on Function.prototype, we're pretty much at the same place you've arrived but without new keywords.

Ah I missed this. I once tried to implement coroutines in v8 but v8 makes use of getspecific and setspecific pthread methods which makes it more complicated.