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.
Small stuff like this really bother some people and they fly off to Pythonland never to be seen again.