Except REPLs are CLIs on steroids.
UNIX shells can only seem powerful for those that never had the luxury of playing with Smalltalk, Lisp, Mesa/Cedar or Oberon environments.
Where you have a CLI and GUI experiences interact together to create a composable workflow experience.
Where I can do function composition on my REPL over data that I just selected with my mouse on a word processor, just to give a possible example.
Where public functions from dynamic modules are exposed on the REPL and can take part in any set of commands.
There is this primitive notion that a CLI needs to be the UNIX way, when a REPL as CLI is so much more powerful.
IPython already makes for a pretty good bash/zsh/etc replacement for many things. You can get a GUI using the IPython notebooks as well.
While I haven't made the switch completely yet, I always keep an IPython session around in an extra tab, since it is very often just much simpler to do something there than in bash.
>I always keep an IPython session around in an extra tab
By "tab" you mean tab in your web browser; do you not? (I ask because there are non-web-based IPython thingies.)
I actually meant a terminal tab (I'm using Tilda as terminal emulator). I'm only really using the web-based notebook interface when I need to display graphics for something.
Just because it's old, doesn't mean it's only about nostalgia.
Besides, I for one can't have this kind of nostalgia because in the '70, my fingers were a bit too short.
There is something extremely convenient to be able to use the same environment everywhere, with minimum prerequisites, because terminal emulation software is very common (probably as common as Web browsers).
I also find it more natural to deal with the system with a CLI when you spend your time editing source code or doing sysadmin stuff; it doesn't break the flow. Of course it's totally different if you're a graphic artist or a Web developer.
Sometimes CLI makes more sense, sometimes GUI makes more sense. But accusing people of being stuck in the past, that makes no sense.