There's an update to for January: http://discuss.ocaml.org/t/multicore-ocaml-january-2020-upda...

Behind the scenes there's a lot of work happening. Retrofitting parallelism to an existing runtime while maintaining compatibility with existing code and keeping the kind of performance users are used to is difficult.

There will be a lot more information out in the next month or two about how it all works, which should coincide with getting more of it upstream.

I don't speak for OCaml or OCaml Labs but am a contributor to multicore if people have specific questions, I can try to answer them.