I use scsh every day, not interactively but the scripts that implement my workflow are written in scsh. I don't change them all that often but when have to tweak something or add a command it's an absolute delight. Imagine -- a shell language with decent power of abstraction.

Here's the main script I use, as an example of practial scsh (I don't know if it would be considered idiomatic): https://github.com/plesner/scsh/blob/master/ash