The blog post gives the rationale; it's a combination of performance, a hope that static typing would make it possible to avoid a class of errors 0install had been experiencing, and wanting to ship native binaries with no dependencies - a pretty specialized use case, but one that 0install happens to need. (I'm aware that things like freeze exist, but they're not really first-class citizens, and the startup time - very important for a command-line utility - is not great).

In general I agree with you, I was a big fan of Python until I discovered Scala. But it's not a great fit for the 0install use case, and as you'll see from subsequent posts, switching to OCaml turned out to increase reliability and performance without sacrificing concision or development productivity.

> With the exception of speed, why does Python need a replacement?

Depends what you use it for. It's very good for a subcategory of problems, in particular prototypes or glue code. However, it leads to "use your test suite as a compiler" for large scale projects due its lack of static typing.

> In my experience developer productivity is of far more importance to business than language performance

You seem to be assuming that Nimrod would necessarily be less productive to work with than Python?