Does anybody think ReasonML will become more popular than plain OCaml outside of front end web development?
Yes.
Just because of FB support, or are there other reasons?
I think because of community interest and the need for a good general-purpose, efficient language. Here are some interesting community-developed projects:
- A cross-platform native-compiling GUI library with a React-influenced design: https://github.com/revery-ui/revery
- A lightning-fast Node version manager: https://github.com/Schniz/fnm
- Erlang-like multicore actors: https://github.com/ostera/reactor
That said, it's early days and the ecosystem has to (and will) mature a lot.