I have started playing with Rust and have used OCaml on and off, but recently really diving hard into it building a REST-based application from top to bottom in OCaml, including all the infrastructure bits. We are slowly making our stuff open source as it becomes useable: https://github.com/afiniate
In short, OCaml is a mature language that has been used for decades in commercial applications. I feel OCaml is the next progression for the people that got excited about distributed systems via the Erlang path and want more of the safety and reasoning that comes from a strongly/statically-typed language like OCaml. Rust may or may not take off, but I am confident OCaml will remain viable for the foreseeable future, and probably gain slow, but steady popularity as engineers see all the cool things you can do like MirageOS: http://openmirage.org/
In short, OCaml is a mature language that has been used for decades in commercial applications. I feel OCaml is the next progression for the people that got excited about distributed systems via the Erlang path and want more of the safety and reasoning that comes from a strongly/statically-typed language like OCaml. Rust may or may not take off, but I am confident OCaml will remain viable for the foreseeable future, and probably gain slow, but steady popularity as engineers see all the cool things you can do like MirageOS: http://openmirage.org/