That makes more sense to me now why doing server side reason compiles to a node.js app and not a more performant OCaml app. Server is not a priority yet.
Server side reason can already compile to native binaries (thanks to the OCaml compiler). While maybe smaller than the npm ecosystem there are a lot of high quality packages available on the OCaml ecosystem [1] that allow for a very pleasant server side development experience. For example https://github.com/rgrinberg/opium is a really nice high level toolkit. There are database bindings to Postgres, Mysql and the like, and high level interfaces to them like https://github.com/paurkedal/ocaml-caqti
[1] http://opam.ocaml.org/packages/