Why? The two technical justifications (objects all the way, and enumeration) in the FLOSS interview [0] are both arguable and not nearly convincing enough to justify further fragmentation of the open-source science ecosystem. If I want cleaner semantics, s/python/ruby is at best moving sideways - for the sake of a few keystrokes? Ruby is slower both in the interpreter itself and in the lack of f2py,Cython,Numexpr,PyC…
Some arguments: * Ruby is expressive and flexible in ways that python is not. For example, Rubyvis is flexible enough (or similar enough to javascript at least) to essentially accept protovis (javascript) code directly. I don't think python can do this. * Ruby uses blocks/enumerators instead of 'for' loops. How much programming involves enumeration of one kind or another? * len(array) vs. array.length
Coding is not just getting the computer to do what you want, it is also how you think about it and the form that it takes. 'len(array)' vs. 'array.length' may not matter to most, but it matters to some of us.
The great news is that we can still use scipy when we need to. I'm betting there is room for both projects, especially considering how small sciruby is at the moment.
Ocaml and clojure are great, but have a steeper learning curve; getting non-programming scientists to contribute is far easier in a language like ruby or python.
A beginning-programmer scientist who wants to start writing code to solve problems currently has to 1) code in python or 2) learn ruby and python/scipy or matlab or R in order to do some scientific computing. SciRuby means (eventually) that for most things, novices only have to learn ruby. It is hard to overstate the importance to new programmers of being able to use just one language (at least to start with).
If you like python over ruby, this is easy. If you like ruby over python, it gets old piping all your data over to a python script to use the basic features of scipy.