It's on the roadmap -- See https://github.com/rethinkdb/rethinkdb/issues/223 to track progress.

There is no precise ETA for now though. Feel free to comment on the github issue if you need it. We build our roadmap on the feedback we get from our users : )

I would also point out that it's included in the list of requirements before we declare RethinkDB production-ready (see https://github.com/rethinkdb/rethinkdb/issues/1174).

It's actually listed as a maybe there.