I haven’t looked into it, but since Reason essentially is OCaml and you can convert between them easily, are these improvements not automatically brought to OCaml?
However, unfinished patches cannot be merged into our mainline tree, and this PR https://github.com/ocaml/ocaml/pull/102 needs some attention to rebase it to trunk, and also to get feedback from testers who may have tried the opam switch and have comments. (associated writeup https://arxiv.org/abs/1512.01897)
Help welcome on this particular patch, and other newer ones from Reason that can be ported over to OCaml and submitted as normal feature improvements.
By the way, the above patch is different from the one that ReasonML uses. Realistically, the work done by the Reason team is more recent and actually shipped with the BuckleScript platform, so now the blocker is, which direction does the OCaml compiler want to go in.