Can't all of this be sidestepped and just write standard (non-forked) OCaml and feed its bytecode through Js_of_ocaml https://ocsigen.org/js_of_ocaml/ ?
That might not have the ultimate React integration (guess that's the answer to the question). But on the other hand probably aligns better with the instinct of many developers to reduce (albeit not eliminate) levels of unnecessary layering.