In frontend? Not 100%, but pretty much.
Elm is a fun new language, it has cool features and its take on FRP is interesting, but I would really like its author to stop speaking like he invented fire.
I would take js_of_ocaml + FRP over Elm any time, just for the size of the ecosystem and the overall expressiveness of the language.
We're looking at the same Elm, right?
As I said, Elm is cute and interesting, but it's type system is less expressive than other languages and lacks features that I consider essential.
Sure, it's better than javascript, but why not opt for the other thing that is even better, given that it also provides Elm's FRP goodness.
The other thing is that Elm comes with the "Elm architecture". A OCaml GUI app backed by the react FRP library comes with "here is an FRP library, figure out the best architecture yourself" architecture. There are other open questions such as "how can I combine this with the hundreds of thousand JS packages on NPM" and "can I use it with Webpack/Typescript/other trendy JS techs".
That said, the possibility of compiling pure-OCaml libraries to JS is quite interesting.
I'd recommend watching this talk: [0]. Evan talks a lot about the decisions that went into the language, such as not having type classes or other advanced features. He makes a strong case for Elm not as a language-to-rule-them-all, but as a tool for the average programmer, who is more interested in building things than in learning about theory. The myriad language features in Haskell, OCaml, etc. are wonderful to those who understand them, but have not proven to be particularly effective at attracting those who aren't already interested in the languages. In that talk, he really made a strong case as to why Elm is valuable and relevant, even for someone such as myself, a functional programming nerd who loves learning about type theory, abstract algebra, and similar things.
Also, I really don't think it's fair to say "The amount of people using Elm right now is a drop in the bucket compared to the amount of people using OCaml (and F#, in more recent years)." OCaml has been around for almost 20 years now, and F# for more than 10. Both have the backing of very large development teams.
ReactiveUI is inspired by functional reactive programming and is the father of the ReactiveCocoa (Cocoa/Swift) framework. Rather than using mutable variables which are replaced and modified in-place, ReactiveUI offers "event streams", represented by the IObserver and IObserverable types, that send values over time.
https://github.com/reactiveui/ReactiveUI http://reactiveui.net/