That's a good question. I think F# and Haskell have stolen a fair amount of OCaml's thunder. Meanwhile, Rust caters to everybody who is tired of C/C++ (putting D in the same position as OCaml, I guess?), while having nice enough constructs that people coming from high-level languages get interested in it. By contrast, OCaml doesn't have the "shiny new" feeling of Rust (also suffers from other issues, such as its standard library/libraries, and the tooling, and the "mlis are documentation" attitude that is fairly prevalent in the community). I'd say with more polish and a lot of marketing, it could easily gain more market share (even though some things have gotten much better since opam).
Sometimes, working in OCaml feels like flying a starship equipped with XVIIIth century cannons. The awesomeness of many of its features is in stark contrast to the gaping holes of its ecosystem (no good INI parsing library in 2014? no usable pure OCaml regexp library?).
Unless you are using CPython extensions, PyPy is usable as a drop-in replacement that's significantly faster in almost all cases. In order to notice any significant speed gain, the JIT needs a chance to "warm up" though, so on short running applications or on web applications for the first couple of requests PyPy can be slower than CPython.
> Does OCaml still doesn't compile 1.0 + 2.0 or has that changed?
I'm not quite sure what you mean? In any case, the compilation speed isn't really an issue (especially since we're talking about Rust, which last time I used it wasn't exactly fast).
Yeah. Honestly it's a quirk, but I prefer quirks going this way than the other way (like universal compare). That said, all languages have warts. And that's the best kind of warts, the one that is explicit and happens at compile-time.
How come, given the amount of use it gets in the industry and academia versus Rust that still hasn't reached 1.0?