The next two years or so will be really exciting.
Rust is beginning to understand that they need more stability and LTS versions, and libraries are blossoming nicely.
Ocaml already has a very mature module ecosystem and is now becoming safe and modern.
I think rust will still have an edge in adoption due to its portrayal as C++ unfucked, but ocaml is definitely the easier tool to work with, imo. And maybe that will change.
I don't think even linear types and multicore would be enough for ocaml to make any significant dent in the systems programming world. Rist and C/C++/D/Zig all do memory management too conveniently, and it opens doors too close to the bottom for ocaml to keep up.
Any ocaml hackers: would you want to write system drivers in ocaml? Why/ why not?
I feel like OCaml is a language that has a lot of potential, but is hampered by somewhat gnarly syntax, a toolchain that feels utterly antique (for example, last time I worked with it, the REPL had no Readline support and had to be run with rlwrap), and lack of a good killer app.
In some ways, OCaml's problem mirror that of Erlang. The gnarly syntax is largely being addressed by Reason (much like Elixir does for Erlang), but I don't see it catching on as much as I'd like, and it still has some warts, I think.
As for killer apps, distributed data processing is something that OCaml could be great at, given that it marries Erlang's functional style with a rich type system, and there was a minor wave of libraries (for concurrent, distributed actor programming) way back in the 2010 or so, but those libraries are now dead and nothing really happened. Meanwhile, Scala largely leads that story (Akka is very popular, and Scala also seems to be the language of choice for Spark, Beam, etc.) and Haskell now has Cloud Haskell, which is modeled on Erlang. Also, we kind of need multicore for this.
(Distributed data is an area where I hope the Java/Scala world gets competition soon. A lot of people, I suspect, would like this, so there's an opportunity to rapidly gain mindshare. I don't see much happening there. Pony is promising (e.g. Wallaroo), and some people have had success with Go (Pachyderm). I don't know Pony, but without genetics, Go is a pretty awkward fit for data pipelines; witness the number of hoops jumped, and resulting limitations, in the Apache Beam SDK for Go. Spark et al rely on distributing bytecode to worker nodes, something you just can't do in Go. Not sure about OCaml.)
Between Opam [1], Dune[2] and utop[3] the "new comer experience" has been really good so far. The editor integration with vim/emacs has been top notch, and visual studio code has turned into a really nice option as well for people who don't like vim/emacs. I'm sure there is still room for improvement, but i'd say its atleast heading in the right direction!
[1] https://github.com/ocaml/opam
[2] https://github.com/ocaml/dune