You use something like bash or zsh when it is convenient rather than to actually do anything with. If you are finding it slow use python, perl ,or something else to do your task; the real power of the shell comes from the easy access to all the unix tools that work well for their singular tasks. That power would be the main criticism I would find with the ruby shell, it seems so foreign and without access to the tools available (unless of course it is using them on the backend) but piping and other one off things would be interesting to see as examples because right now this shell looks like ruby with some libraries added in (sorry not a ruby programmer so I don't know the proper term)