Thanks for sharing these links @kit-ty-kate – I think @brettgilio may already be aware of this. The Multicore prerequisite patches appearing in released OCaml compilers now post is really mainly about https://github.com/ocaml/ocaml/pull/8713 (already mentioned above by me) but I think it would be useful to know if there is anything else after that.
Then again, this is an open source effort and I leave it to the people in-the-know to add any additional info if they can.