If you'd like to see the approach we're taking at OCaml Labs in order to build multicore, read KC's blog post here:

http://kcsrk.info/ocaml/multicore/2015/05/20/effects-multico...

The core idea is incredibly exciting (to us, anyway). Rather than baking in a specific multicore scheduler, we're allowing pluggable schedulers written in OCaml. They use algebraic effects to allow an independent scheduler to compose concurrency among OCaml threads. This will ensure that the OCaml runtime remains lean, and even allow applications to define their own strategies for concurrent scheduling.