Mercury is used in production with PrinceXML [1] and ODASE [2]. ATS is used in production in the implementation of a bitcoin mining pool [3]. OCaml is heavily used by Jane St [4]. SML (via the MLton implementation) is used in industry [5]. Rust is not ready for production, I agree, but is being used to develop Servo by Mozilla and Samsung [6].

That said I'd hope that systems like ATS, Mercury, MLTon and OCaml being open source make it easier to contribute to the implementation for issues that come up and this would offset any 'not enough real world' problems that they have. If you don't like those languages, pick another (eg. Haskell).

[1] http://en.wikipedia.org/wiki/Prince_XML

[2] http://www.missioncriticalit.com/technology.html

[3] http://mmpool.bitparking.com/pool

[4] https://blogs.janestreet.com/category/ocaml/

[5] http://mlton.org/Users

[6] https://blog.mozilla.org/blog/2013/04/03/mozilla-and-samsung...

Actually, it's being "ressurected" through the work of ocamlpro & ocamllabs. The tooling in particular has improved a lot in the last 2 years.