Low effort post? Even though multithreading isn't relevant to the ARM64 work: for the first time in a long time, I think we can see a serious Ocaml multicore in the practical future, not the perennial "some day, maybe." You can already try the pools/futures part of the new multicore implementation, it's the algebraic effects part that is still outstanding -- see:
https://github.com/prismlab/parallel-programming-in-multicor...